Methods for treating cancer

ABSTRACT

Disclosed herein are methods of inhibiting tumor growth or producing tumor regression in a subject by administering to the subject a therapeutically effective amount of a combination of palbociclib and RAD1901.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No. PCT/US2016/030321, filed Apr. 29, 2016, which claims the benefit of U.S. Provisional Application No. 62/154,699, filed Apr. 29, 2015, U.S. Provisional Application No. 62/155,451, filed Apr. 30, 2015, U.S. Provisional Application No. 62/252,085, filed Nov. 6, 2015, U.S. Provisional Application No. 62/265,696, filed Dec. 10, 2015, U.S. Provisional Application No. 62/158,469, filed May 7, 2015, U.S. Provisional Application No. 62/252,916, filed Nov. 9, 2015, U.S. Provisional Application No. 62/265,774, filed Dec. 10, 2015, U.S. Provisional Application No. 62/192,940, filed Jul. 15, 2015, U.S. Provisional Application No. 62/265,658, filed Dec. 10, 2015, U.S. Provisional Application No. 62/323,572, filed Apr. 15, 2016, U.S. Provisional Application No. 62/192,944, filed Jul. 15, 2015, U.S. Provisional Application No. 62/265,663, filed Dec. 10, 2015, and U.S. Provisional Application No. 62/323,576, filed Apr. 15, 2016, all of which are incorporated herein by reference in their entireties.

BACKGROUND

Breast cancer is divided into three subtypes based on expression of three receptors: estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor-2 (Her2). Overexpression of ERs is found in many breast cancer patients. ER-positive (ER+) breast cancers comprise two-thirds of all breast cancers. Other than breast cancer, estrogen and ERs are associated with, for example, ovarian cancer, colon cancer, prostate cancer and endometrial cancer.

ERs can be activated by estrogen and translocate into the nucleus to bind to DNA, thereby regulating the activity of various genes. See, e.g., Marino et al., “Estrogen Signaling Multiple Pathways to Impact Gene Transcription,” Curr. Genomics 7(8): 497-508 (2006); and Heldring et al., “Estrogen Receptors: How Do They Signal and What Are Their Targets,” Physiol. Rev. 87(3): 905-931 (2007).

Agents that inhibit estrogen production, such as aromatase inhibitors (AIs, e.g., letrozole, anastrozole and aromasin), or those that directly block ER activity, such as selective estrogen receptor modulators (SERMs, e.g., tamoxifen, toremifene, droloxifene, idoxifene, raloxifene, lasofoxifene, arzoxifene, miproxifene, levormeloxifene, and EM-652 (SCH 57068)) and selective estrogen receptor degraders (SERDs, e.g., fulvestrant, TAS-108 (SR16234), ZK191703, RU58668, GDC-0810 (ARN-810), GW5638/DPC974, SRN-927, ICI182782 and AZD9496), have been used previously or are being developed in the treatment of ER-positive breast cancers.

SERMs (e.g., tamoxifen) and AIs are often used as a first-line adjuvant systemic therapy for ER-positive breast cancer. Tamoxifen is commonly used for ER-positive breast cancer. AIs suppress estrogen production in peripheral tissues by blocking the activity of aromatase, which turns androgen into estrogen in the body. However, AIs cannot stop the ovaries from making estrogen, Thus, AIs are mainly used to treat postmenopausal women. Furthermore, as AIs are much more effective than tamoxifen with fewer serious side effects, AIs may also be used to treat premenopausal women with their ovarian function suppressed. See, e.g., Francis et al., “Adjuvant Ovarian Suppression in Premenopausal Breast Cancer,”N Engl. J. Med, 372:436-446 (2015).

While initial treatment with these agents may be successful, many patients eventually relapse with drug-resistant breast cancers. Mutations affecting the ER have emerged as one potential mechanism for the development of this resistance. See, e.g., Robinson et al., “Activating ESR1 mutations in hormone-resistant metastatic breast cancer,” Nat. Genet. 45:1446-51 (2013). Mutations in the ligand-binding domain (LBD) of ER are found in 21% metastatic ER-positive breast tumor samples from patients who received at least one line of endocrine treatment. Jeselsohn, et al., “ESR1 mutations—a mechanism for acquired endocrine resistance in breast cancer,” Nat. Rev. Clin. Oncol., 12:573-83 (2015).

Fulvestrant is currently the only SERD approved for the treatment of ER-positive metastatic breast cancers with disease progression following antiestrogen therapy. Despite its clinical efficacy, the utility of fulvestrant has been limited by the amount of drug that can be administered in a single injection and by reduced bioavailability. Imaging studies using 18F-fluoroestradiol positron emission tomography (FES-PET) suggest that even at the 500 mg dose level, some patients may not have complete ER inhibition, and insufficient dosing may be a reason for therapeutic failure.

Another challenge associated with estrogen-directed therapies is that they may have undesirable effects on uterine, bone, and other tissues. The ER directs transcription of estrogen-responsive genes in a wide variety of tissues and cell types. These effects can be particularly pronounced as endogenous levels of estrogen and other ovarian hormones diminish during menopause. For example, tamoxifen can cause bone thinning in premenopausal women and increase the risk of endometrial cancer because it acts as a partial agonist on the endometrium. In postmenopausal women, AIs can cause more bone loss and more broken bones than tamoxifen. Patients treated with fulvestrant may also be exposed to the risk of osteoporosis due to its mechanism of action.

Cell cycle regulators such as cyclins and cyclin-dependent kinases (CDKs) have been reported to have effects on ER expression. Lamb et al., “Cell cycle regulators cyclin D1 and CDK4/6 have estrogen receptor-dependent divergent functions in breast cancer migration and stem cell-like activity,” Cell Cycle 12(15): 2384-2394 (2013). Selective CDK4/6 inhibitors (e.g., ribociclib, abemaciclib and palbociclib) have enabled tumor types in which CDK4/6 has a pivotal role in the G1-to-S-phase cell cycle transition to be targeted with improved effectiveness and fewer adverse effects to normal cells. O'Leary et al., “Treating cancer with selective CDK4/6 inhibitors,” Nat. Rev. Clin. Oncol. (2016), published online 31 Mar. 2016 (http://www.nature.com/nrclinonc/journal/vaop/ncurrent/full/nrclinonc.2016.26.html). The selective CDK4/6 inhibitors demonstrated the best responses when tested in combination with endocrine therapy in patients with ER-positive breast cancer.

Palbociclib in combination with the aromatase inhibitor letrozole (PALoMA-1/TRIO 18 study) was approved for the treatment of hormone receptor (HR)-positive (HR+), HER2− negative (HER2−) advanced breast cancer as initial endocrine based therapy in postmenopausal women in February 2015. In February 2016, palbociclib in combination with the SERD fulvestrant (PALOMA-3 study) was approved for the treatment of ER+, HER2− advanced or metastatic breast cancer patients that had progressed on prior endocrine therapy. The FDA has granted the CDK4/6 inhibitor abemaciclib (LY2835219) a breakthrough therapy designation as monotherapy for heavily pretreated patients with refractory HR-positive advanced breast cancer, based on data from a phase I study (JPBA study). Additional combinations of selective CDK4/6 inhibitors (e.g., ribociclib, abemaciclib and palbociclib) with endocrine therapies (e.g., AIs, SERMs and SERDs) are currently under development.

However, CDK4/6 inhibitors demonstrate toxicities that may require intermittent therapy (O'Leary). Furthermore, there remains a need for more durable and effective ER-targeted therapies that can overcome challenges associated with the current endocrine therapies, while providing additional benefits by combining with CDK4/6 inhibitors to combat cancer in advanced stage and/or with resistance to prior treatments.

BRIEF DESCRIPTION OF DRAWINGS AND TABLES

This application contains at least one drawing executed in color. Copies of this application with color drawing(s) will be provided by the Office upon request and payment of the necessary fees.

FIG. 1. RAD1901-palbociclib combination showed improved tumor growth inhibition (TGI) compared to RAD1901 single agent treatment in various patient-derived xenograft (PDx) models regardless of ESR1 status and prior endocrine therapy. Percentage of TGI in PDx models treated with RAD1901 alone or in combination with palbociclib is shown.

FIGS. 2A-C. The combination of RAD1901 and palbociclib demonstrated tumor growth inhibition and regression in wild-type (WT) ERa MCF-7 xenograft models (PR+, HER2−). (A): Tumor growth of MCF-7 xenograft models treated with vehicle control, palbociclib (45 mg/kg, p.o., q.d), fulvestrant (3 mg/dose, s.c., qwk), a combination of fulvestrant (3 mg/dose, s.c., qwk) and palbociclib (45 mg/kg, p.o., q.d), RAD1901 (60 mg/kg, p.o., q.d.), and a combination of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (45 mg/kg, p.o., q.d); One-way ANOVA, “ns” is not significant, *p-value<0.05, and ***p-value<0.001; (B): Change in individual tumor size from baseline to end of study of MCF-7 xenograft models treated with vehicle control, palbociclib (45 mg/kg, p.o., q.d), fulvestrant (3 mg/dose, s.c., qwk), a combination of fulvestrant (3 mg/dose, s.c., qwk) and palbociclib (45 mg/kg, p.o., q.d), RAD1901 (60 mg/kg, p.o., q.d.), and combinations of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (45 mg/kg, p.o., q.d); (C): Tumor growth of MCF-7 xenograft models treated with vehicle control, palbociclib (45 mg/kg, p.o., q.d), fulvestrant (3 mg/dose, s.c., qwk), a combination of fulvestrant (3 mg/dose, s.c., qwk) and palbociclib (45 mg/kg, p.o., q.d), RAD1901 (30 or 60 mg/kg, p.o., q.d.), and a combination of RAD1901 (30 or 60 mg/kg, p.o., q.d.) and palbociclib (45 mg/kg, p.o., q.d).

FIGS. 3A-B. The combination of RAD1901 and palbociclib demonstrated tumor growth inhibition and regression in WT ERa PDx-11 models (PR+, Her2+, previously treated with aromatase inhibitor, fulvestrant, and chemotherapy). (A): Tumor growth of PDx-11 models treated with vehicle control, fulvestrant (3 mg/dose, s.c., qwk), palbociclib (45 mg/kg, p.o., q.d), RAD1901 (60 mg/kg, p.o., q.d.), and a combination of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (45 mg/kg, p.o., q.d); (B): Change in individual tumor size from baseline to end of study in PDx-11 models treated with vehicle control, fulvestrant (3 mg/dose, s.c., qwk), RAD1901 (60 mg/kg, p.o., q.d.), and a combination of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (45 mg/kg, p.o., q.d). n=8-10/group.

FIGS. 4A-B. The combination of RAD1901 and palbociclib demonstrated tumor growth inhibition in WT ER+PDx-2 models (PR+, Her2+, treatment naïve). (A): Tumor growth of PDx-2 models treated with vehicle control, RAD1901 (60 mg/kg, p.o., q.d.), fulvestrant (3 mg/dose, s.c., qwk), and a combination of RAD1901 (60 mg/kg, p.o., q.d.) and fulvestrant (3 mg/dose, s.c., qwk); (B): Tumor growth of PDx-2 models treated with vehicle control, palbociclib (75 mg/kg, p.o., q.d), RAD1901 (60 mg/kg, p.o., q.d.), and a combination of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (75 mg/kg, p.o., q.d). n=8-10/group.

FIG. 5. Efficacy of RAD1901 sustained at least two months after RAD1901 treatment ended while estradiol treatment continued in WT ERα PDx-4 models (PR+, Her2+, treatment naïve).

FIGS. 6A-C. The combination of RAD1901 and palbociclib demonstrated tumor growth inhibition in mutant (Y537S) ERa PDx-5 models (PR+, Her2+, previously treated with aromatase inhibitors). (A): Tumor growth of PDx-5 models treated with vehicle control, fulvestrant (3 mg/dose, s.c., qwk), RAD1901 (60 mg/kg, p.o., q.d.), palbociclib (75 mg/kg, p.o., q.d), and a combination of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (75 mg/kg, p.o., q.d); (B): Change in individual tumor size from baseline to day 17 for fulvestrant (3 mg/dose, s.c., qwk), palbociclib (75 mg/kg, p.o., q.d), and a combination of RAD1901 (60, 120 mg/kg, p.o., q.d.) and palbociclib (75 mg/kg, p.o., q.d); and (C) Change in individual tumor size from baseline to day 56 for palbociclib (75 mg/kg, p.o., q.d), RAD1901 (60, 120 mg/kg, p.o., q.d.) and a combination of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (75 mg/kg, p.o., q.d). n=8-10/group.

FIGS. 7A-B. The combination of RAD1901 and palbociclib demonstrated tumor growth inhibition in mutant (Y537S) ERα PDx-5 models (PR+, Her2+, previously treated with aromatase inhibitors). (A): Tumor growth of PDx-5 models treated with vehicle control, fulvestrant (3 mg/dose, s.c., qwk), RAD1901 (60 mg/kg, p.o., q.d.), palbociclib (p.o., q.d), and a combination of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (p.o., q.d); (B): Tumor growth of PDx-5 models treated with vehicle control, fulvestrant (3 mg/dose, s.c., qwk), RAD1901 (120 mg/kg, p.o., q.d.), palbociclib (p.o., q.d), and a combination of RAD1901 (120 mg/kg, p.o., q.d.) and palbociclib (p.o., q.d).

FIG. 8. The combination of RAD1901 and palbociclib demonstrated tumor growth inhibition in mutant (Y537S) ERα PDx-5 models (PR+, Her2+, previously treated with aromatase inhibitors). Tumor growth of PDx-5 models treated with vehicle control, fulvestrant (3 mg/dose, s.c., qwk), RAD1901 (60 mg/kg, p.o., q.d.), palbociclib (75 mg, p.o., q.d), a combination of fulvestrant (3 mg/dose, s.c., qwk) and palbociclib (75 mg, p.o., q.d), and a combination of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (75 mg, p.o., q.d). n=8-10/group.

FIG. 9. Pharmacokinetic analysis of fulvestrant in nude mice. The plasma concentration of fulvestrant at 1 mg/dose (solid diamond), 3 mg/dose (solid circle), and 5 mg/dose (solid triangle) is shown. The nude mice were dosed subcutaneously with fulvestrant on Day 1 and the second dose on Day 8. The plasma concentration of fulvestrant was monitored at the indicated time points for up to 168 hours after the second dose.

FIG. 10. Effect of RAD1901 and fulvestrant (Faslodex) on mouse survival in an intracranial MCF-7 tumor model.

FIGS. 11A-C. A representative image of FES-PET scan of the uterus of a subject treated with 200 and 500 mg RAD1901 p.o., q.d., and change of the ER engagement after the RAD1901 treatments. (A): Transversal view of uterus CT scan before 200 mg RAD1901 treatment (a) and after (c), and transversal view of uterus FES-PET scan before the RAD1901 treatment (b) and after (d); (B): Sagittal view of uterus CT scan before 500 mg RAD1901 treatment (top (a) panel) and after (bottom (a) panel), sagittal view of uterus FES-PET scan before the RAD1901 treatment (top (b) panel) and after (bottom (b) panel), transversal view of uterus CT scan before the RAD1901 treatment (top (c) panel) and after (bottom (c) panel), transversal view of uterus FES-PET scan before the RAD1901 treatment (top (d) panel) and after (bottom (d) panel); (C): % change of ER engagement after the RAD1901 treatments of Subjects 1-3 (200 mg) and Subjects 4-7 (500 mg) compared to baseline (before RAD1901 treatment).

FIGS. 12A-B. A representative image of FES-PET scan of the uterus (A) and pituitary (B) before (Baseline) and after (Post-treatment) RAD1901 treatment (500 mg). (a) Lateral cross-section; (b) longitude cross-section; and (c) longitude cross-section.

FIG. 13. PR and ER expression in MCF-7 xenograft models treated with vehicle control, RAD1901, palbociclib, a combination of RAD1901 and palbociclib, fulvestrant, and a combination of fulvestrant and palbociclib.

FIGS. 14A-B. RAD1901 treatment resulted in complete ER degradation and inhibited ER signaling in MCF-7 cell lines (A) and T47D cell lines (B) in vitro. The ER expression was shown in both cell lines treated with RAD1901 and fulvestrant at various concentrations of 0.001 μM, 0.01 μM, 0.1 μM and 1 μM, respectively. ER signaling was shown by three ER target genes tested: PGR, GREB1 and TFF1.

FIGS. 15A-C. RAD1901 treatment resulted in ER degradation and abrogation of ER signaling in MCF-7 xenograft models. (A): Western blot showing PR and ER expression in the MCF-7 xenograft models treated with vehicle control, RAD1901 at 30 and 60 mg/kg, and fulvestrant at 3 mg/dose, 2 hour or 8 hour after the last dose; (B): ER protein expression in the MCF-7 xenograft models treated with vehicle control, RAD1901 at 30 and 60 mg/kg, and fulvestrant at 3 mg/dose, 2 hour after the last dose; (C): PR protein expression in the MCF-7 xenograft models treated with vehicle control, RAD1901 at 30 and 60 mg/kg, and fulvestrant at 3 mg/dose, 8 hour after last dose.

FIGS. 16A-C. RAD1901 treatment resulted in a rapid decrease in PR in MCF-7 xenograft models. (A): Western blot showing PR expression in MCF-7 xenograft models treated with vehicle control and RAD1901 at 30, 60, and 90 mg/kg, at 8 hours or 12 hours after single dose; (B): Western blot showing PR expression in MCF-7 xenograft models treated with vehicle control and RAD1901 at 30, 60, and 90 mg/kg, at 4 hours or 24 hours after the 7th dose; (C): Dose-dependent decrease in PR expression in MCF-7 xenograft models treated with RAD1901 at 30, 60, and 90 mg/kg.

FIGS. 17A-B. RAD1901 treatment resulted in a rapid decrease in proliferation in MCF-7 xenograft models. (A): A representative photograph of a sectioned tumor harvested from MCF-7 xenograft models treated with vehicle control and RAD1901 at 90 mg/kg, 8 hours after single dose and 24 hours after the 4th dose, stained for proliferation marker Ki-67; (B): Histogram showing decrease of proliferation marker Ki-67 in MCF-7 xenograft models treated with vehicle control and RAD1901 at 90 mg/kg, 8 hours after single dose and 24 hours after the 4th dose.

FIG. 18. RAD1901 treatment at 30, 60, and 120 mg/kg decreased Ki67 more significantly than fulvestrant (1 mg/animal) in end of study tumors of PDx-4 models four hours on the last day of a 56 day efficacy study.

FIG. 19. RAD1901 treatment at 60 and 120 mg/kg resulted in reduced ER signaling in vivo in PDx-5 models with decreased PR expression.

FIGS. 20A-D. Effect of RAD1901 on uterine tissue in newly weaned female Sprague-Dawley rats. (A): Uterine wet weights of rats euthanized 24 hours after the final dose; (B): Epithelial height in tissue sections of the uterus; (C): Representative sections of Toluidine Blue O-stained uterine tissue at 400× magnification, arrows indicate uterine epithelium; (D): Total RNA extracted from uterine tissue and analyzed by quantitative RT-PCR for the level of complement C3 expression relative to the 18S ribosomal RNA housekeeping gene.

FIG. 21. Plasma pharmacokinetic results of RAD1901 at 200, 500, 750, and 1000 mg/kg after dosing on Day 7.

FIG. 22. 3ERT (I).

FIG. 23. 3ERT (II).

FIG. 24. Superimpositions of the ERα LBD-antagonist complexes summarized in Table 10.

FIGS. 25A-B. Modeling of (A) RAD1901-1R5K; and (B) GW5-1R5K.

FIGS. 26A-B. Modeling of (A) RAD1901-1SJ0; and (B) E4D-1SJ0.

FIGS. 27A-B. Modeling of (A) RAD1901-2JFA; and (B) RAL-2JFA.

FIGS. 28A-B. Modeling of (A) RAD1901-2BJ4; and (B) OHT-2BJ4.

FIGS. 29A-B. Modeling of (A) RAD1901-2IOK; and (B) IOK-2IOK.

FIG. 30. Superimpositions of the RAD1901 conformations resulted from IFD analysis with 1R5K and 2OUZ.

FIG. 31. Superimpositions of the RAD1901 conformations resulted from IFD analysis with 2BJ4, and 2JFA.

FIGS. 32A-B. Superimpositions of the RAD1901 conformations resulted from IFD analysis with 2BJ4, 2JFA and 1SJ0.

FIGS. 33A-C. IFD of RAD1901 with 2BJ4.

FIGS. 34A-C. Protein Surface Interactions of RAD1901 docked in 2BJ4 by IFD.

FIGS. 35A-C. IFD of Fulvestrant with 2BJ4.

FIGS. 36A-B. IFD of Fulvestrant and RAD1901 with 2BJ4.

FIGS. 37A-B. Superimposions of IFD of Fulvestrant and RAD1901 with 2BJ4.

FIG. 38. RAD1901 in vitro binding assay with ERα constructs of WT and LBD mutant.

FIG. 39. Location of exemplary mutations of ERα and frequencies thereof.

Table 1. RAD1901 levels in plasma, tumor and brain of mice implanted with MCF7 cells after treated for 40 days.

Table 2. SUV for uterus, muscle, and bone for a human subject treated with 200 mg dose p.o., q.d., for six days.

Table 3. SUV for uterus, muscle, and bone for a human subjects (n=4) treated with 500 mg dose p.o., q.d., for six days.

Table 4. Effect of RAD1901 on BMD in ovariectomized rats. Adult female rats underwent either sham or ovariectomy surgery before treatment initiation with vehicle, E2 (0.01 mg/kg) or RAD1901 (3 mg/kg) q.d. (n=20 per treatment group). BMD was measured by dual emission x-ray absorptiometry at baseline and after 4 weeks of treatment. Data are expressed as mean±SD. *P<0.05 versus the corresponding OVX+Veh control. BMD, bone mineral density; E2, beta estradiol; OVX, ovariectomized; Veh, vehicle.

Table 5. Effect of RAD1901 on femur microarchitecture in ovariectomized rats. Adult female rats underwent either sham or ovariectomy surgery before treatment initiation with vehicle, E2 (0.01 mg/kg) or RAD1901 (3 mg/kg) q.d. (n=20 per treatment group). After 4 weeks, Bone microarchitecture was evaluated using microcomputed tomography. Data are expressed as mean±SD. *P<0.05 versus the corresponding OVX+Veh control. ABD, apparent bone density; BV/TV, bone volume density; ConnD, connectivity density; E2, beta estradiol; OVX, ovariectomized; TbN, trabecular number; TbTh, trabecular thickness; TbSp, trabecular spacing; Veh, vehicle.

Table 6. Key baseline demographics of Phase 1 dose escalation study of RAD1901.

Table 7. Most frequent (>10%) treatment related AEs in a Phase 1 dose escalation study of RAD1901. AEs graded as per CTCAE v4.0. Any patient with multiple scenarios of a same preferred term was counted only once to the most severe grade. *>10% of patients in the total active group who had any related TEAEs. N=number of subjects with at least one treatment-related AE in a given category.

Table 8. Pharmacokinetic parameters in a Phase 1 dose escalation study of RAD1901 (Day 7).

Table 8. Pharmacokinetic parameters in a Phase 1 dose escalation study of RAD1901 (Day 7).

Table 9. Frequency of LBD mutations.

Table 10. Differences of ER-α LBD-antagonist complexes in residue poses versus 3ERT.

Table 11. Evaluation of structure overlap of ER-α LBD-antagonist complexes by RMSD calculations.

Table 12. Analysis of ligand binding in ER-α LBD-antagonist complexes.

Table 13. Model evaluation for RAD1901 docking.

Table 14. Induced Fit Docking Score of RAD1901 with 1R5K, 1SJ0, 2IFA, 2BJ4 and 2OUZ.

DETAILED DESCRIPTION OF THE INVENTION

As set forth in the Examples section below, a combination of RAD1901 and palbociclib (a RAD1901-palbo combination) (structures below) demonstrated greater tumor growth inhibition than RAD1901 alone in breast cancer xenograft models, regardless of ESR1 status, PR status and prior endocrine therapy (Example I(A)). The xenograft models treated had tumor expressing wild-type (WT) or mutant (e.g., Y537S) ERa, with or without PR expression, with high or low Her2 expression, and with or without prior endocrine therapy (e.g., tamoxifen (tam), AI, fulvestrant), chemotherapy (chemo), Her2 inhibitors (Her2i, e.g., trastuzumab, lapatinib), bevacizumab, and/or rituximab (FIG. 1). RAD1901-palbo combinations showed greater tumor growth inhibition (TGI of 65% or higher) in xenograft models wherein RAD1901 alone achieved a TGI of 26-64%; and RAD1901-palbo combinations showed greater tumor growth inhibition (TGI of 26-64%) in xenograft models wherein RAD1901 alone achieved a TGI of less than 25%. RAD1901-palbo combinations showed greater tumor regression than RAD1901 alone in xenograft models that are highly responsive to RAD1901 treatment (TGI of 65% or higher), e.g., PDx-11 (FIGS. 3A-B)

ER WT PDx models and ER mutant PDx models may have different level of responsiveness to treatment with fulvestrant alone, palbociclib alone, and/or a combination of fulvestrant and palbociclib (a ful-palbo combination). However, RAD1901-palbo combinations demonstrated improved tumor growth inhibition and/or tumor regression compared to treatment with RAD1901 alone or palbociclib alone, regardless of whether the PDx models were responsive to fulvestrant treatment and/or ful-palbo combination treatment. In other words, RAD1901-palbo combination may inhibit tumor growth and/or produce tumor regression in fulvestrant resistant cancers.

RAD1901-palbo combination treatment demonstrated improved tumor growth inhibition and/or tumor regression compared to treatment with fulvestrant alone or with the ful-palbo combination. For example, the RAD1901-palbo combination caused more significant tumor regression in more WT ER+xenograft models than treatment with fulvestrant alone, RAD1901 alone, or palbociclib alone, even though these xenograft models have varied responsiveness to fulvestrant treatment (e.g., MCF7 cell line xenograft model responsive to fulvestrant treatment (FIGS. 2A-C); PDx-11 model responsive to fulvestrant treatment (FIGS. 3A-B); and PDx-2 model least responsive to fulvestrant treatment (FIGS. 3A-B)). The RAD1901-palbo combination also caused more significant tumor regression in more WT ER+MCF7 cell line xenograft models and PDx-11 models than treatment with a ful-palbo combination (FIGS. 2A-C and 3A-B). The RAD1901-palbo combination provided similar effects with RAD1901 at a dose of 30 mg/kg or 60 mg/kg, although RAD1901 alone at 30 mg/kg was not as effective as RAD1901 alone at 60 mg/kg in inhibiting tumor growth (FIG. 2C). Said results suggest a RAD1901-palbo combination with a lower dose of RAD1901 (e.g., 30 mg/kg) was sufficient to maximize the tumor growth inhibition/tumor regression effects in said xenograft models.

The RAD1901-palbo combination demonstrated tumor regression or improved tumor growth inhibition in mutant ER+(e.g., Y537S) PDx models hardly responsive to fulvestrant treatment. For example, PDx-5 is an ER Y537S mutant PDx model (PR+, Her2+, prior treatment with AI) hardly responsive to fulvestrant treatment. RAD1901-palbo combination demonstrated tumor regression in PDx-5 model, while palbociclib alone or RAD1901 alone only inhibited tumor growth without causing tumor regression (FIGS. 6A-C and 7A-B). Furthermore, the RAD1901-palbo combination provided similar effects with RAD1901 at a dose of 60 mg/kg or 120 mg/kg (FIGS. 7A-B), suggesting a RAD1901-palbo combination with a lower dose of RAD1901 (e.g., 60 mg/kg) was sufficient to maximize the tumor growth inhibition/tumor regression effects in said PDx models. The RAD1901-palbo combination caused more significant tumor growth inhibition than RAD1901 alone, palbociclib alone, fulvestrant alone, or the ful-palbo combination in mutant PDx-5 models (FIG. 8). Unexpectedly, the ful-palbo combination did not enhance tumor growth inhibition significantly compared to treatment with palbociclib alone in PDx-5 models (FIG. 8). Thus, the addition of fulvestrant did not benefit the PDx-5 models when applied in combination with palbociclib, while the additional of RAD1901 unexpectedly did. Furthermore, the longer the treatment, the more significant tumor growth inhibition the RAD1901-palbo combo achieved when compared to RAD1901 treatment alone or palbociclib treatment alone (FIG. 8). Thus, RAD1901-palbo combinations provide powerful anti-tumor therapy for ER+ breast cancer expressing WT or mutant ER, with or without PR expression, with high or low Her2 expression, and with or without resistance to fulvestrant.

The results provided herein also show that RAD1901 can be delivered to the brain (Example II), and said delivery improved mouse survival in an intracranial tumor model expressing wild-type ERα (MCF-7 xenograft model, Example I(B)). As palbociclib has been reported to cross the brain-blood barrier (O'Leary), a RAD1901-palbo combination is likely to also be able to cross brain-blood bather and treat ER+ tumors in brain. This represents an additional advantage over the ful-palbo combination for treating ER+ tumors in the brain, as fulvestrant cannot cross the blood-brain barrier (Vergotel et al., “Fulvestrant, a new treatment option for advanced breast cancer: tolerability versus existing agents,” Ann. Oncol., 17(2):200-204 (2006)). A combination of RAD1901 with other CDK4/6 inhibitor(s) that can cross the blood-brain barrier (e.g., abemaciclib (O'Leary)) may also have similar therapeutic effects on ER+ tumors in brain.

RAD1901 showed sustained efficacy in inhibiting tumor growth after treatment ended while estradiol treatment continued (e.g., PDx-4 model). Thus, a RAD1901-palbo combination is likely to benefit patients by inhibiting tumor growth after treatment ends, especially when CDK4/6 inhibitors (e.g., ribociclib, abemaciclib and palbociclib) can only be administered intermittently due to their side effects (O'Leary).

A RAD1901-palbo combination is likely to have lower side-effects than treatment with palbociclib alone or a combination of palbociclib with other hormone therapies (e.g., AIs such as letrozole and SERDs such as fulvestrant). For example, both AIs and fulvestrant may cause bone loss in treated patients. RAD1901 is unlikely to have similar side effects. RAD1901 was found to preferentially accumulate in tumor, with a RAD1901 level in tumor v. RAD1901 level in plasma (T/P ratio) of up to about 35 (Example II). Standardized uptake values (SUV) for uterus, muscle and bone were calculated for human subjects treated with RAD1901 at a dose of about 200 mg up to about 500 mg q.d. (Example III(A)). Post-dose uterine signals were close to levels from “non-target tissues” (tissues that do not express estrogen receptor), suggesting a complete attenuation of FES-PET uptake post-RAD1901 treatment. Almost no change was observed in pre-versus post-treatment PET scans in tissues that did not significantly express estrogen receptor (e.g., muscles, bones) (Example IIIA). Finally, RAD1901 treatments antagonized estradiol stimulation of uterine tissues in ovariectomized (OVX) rats (Example IV(A)), and largely preserved bone quality of the treated subjects. For example, OVX rats treated with RAD1901 showed maintained BMD and femur microarchitecture (Example IV(A)). Thus, the RAD1901-palbo combination may be especially useful for patients having osteoporosis or a higher risk of osteoporosis.

Furthermore, RAD1901 was found to degrade wild-type ERα and abrogate ER signaling in vivo in MCF7 cell line xenograft models, and showed a dose-dependent decrease in PR in these MCF7 cell line xenograft models (Example III(B)). RAD1901 decreased proliferation in MCF7 cell line xenograft models and PDx-4 models as evidenced by a decrease in proliferation marker Ki67 in tumors harvested from the treated subjects. RAD1901 also decreased ER signaling in vivo in an ER mutant PDx model that was hardly responsive to fulvestrant treatment (Example III(B)).

The unexpected efficacy of RAD1901-palbo combination in tumors hardly responsive to fulvestrant treatments and in tumors expressing mutant ERα may be due to the unique interactions between RAD1901 and ERa. Structural models of ERα bound to RAD1901 and other ERa-binding compounds were analyzed to obtain information about the specific binding interactions (Example V). Computer modeling showed that RAD1901-ERα interactions are not likely to be affected by mutations in the LBD of ERa, e.g., Y537X mutant wherein X was S, N, or C; D538G; and S463P, which account for about 81.7% of LBD mutations found in a recent study of metastatic ER positive breast tumor samples from patients who received at least one line of endocrine treatment (Table 9, Example V). Thus, a combination of one or more CDK4 and/or CDK6 inhibitors as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof is likely to have therapeutic effects with relatively low side effects similar to RAD1901-palbo combinations as disclosed herein. The computer modeling resulted in identification of specific residues in the C-terminal ligand-binding domains of ERα that are critical to binding, information that can be used to develop compounds that bind and antagonize not only wild-type ERα but also certain mutants and variants thereof, which when combined with a CDK4/6 inhibitor (e.g., ribociclib, abemaciclib and palbociclib) may provide strong anti-tumor therapy with relatively low side effects similar to RAD1901-palbo combinations as disclosed herein.

Based on these results, methods are provided herein for inhibiting growth or producing regression of an ERa-positive tumor in a subject in need thereof by administering to the subject a therapeutically effective amount of a combination of RAD1901 or solvates (e.g., hydrate) or salts thereof and one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib). In certain embodiments, administration of RAD1901 or solvates (e.g., hydrate) or salts thereof has additional therapeutic benefits in addition to inhibiting tumor growth, including for example inhibiting cancer cell proliferation or inhibiting ERα activity (e.g., by inhibiting estradiol binding or by degrading ERa). In certain embodiments, the method does not provide negative effects to muscles, bones, breast, and/or uterus.

In certain embodiments, RAD1901 or solvates (e.g., hydrate) or salts thereof modulates and/or degrades ERα and mutant ERα.

In certain embodiments of the tumor growth inhibition or tumor regression methods provided herein, methods are provided for inhibiting growth or producing regression of an ERα-positive tumor in a subject in need thereof by administering to the subject a therapeutically effective amount of a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or a solvate (e.g., hydrate) or salt thereof. In certain of these embodiments, the salt thereof is RAD1901 dihydrochloride having the structure:

CDK4 and/or CDK6 Inhibitors

In certain embodiments, the CDK4 and/or CDK6 inhibitors include, without limitation, palbociclib, abemaciclib, ribociclib, AMG925, Formula II compounds, Formula III compounds and Formula IV compounds as disclosed below, solvates thereof, salts thereof, and combinations thereof.

Abemaciclib (LY2835219, 2-pyrimidinamine, N-(5-((4-ethyl-1-piperazinyl)methyl)-2-pyridinyl)-5-fluoro-4-(4-fluoro-2-methyl-1-(1-methylethyl)-1H-benzimidazol-6-yl))

Ribociclib, (LEE011, 7-cyclopentyl-N,N-dimethyl-245-(piperazin-1-yppyridin-2-yl)amino)-7H-pyrrolo[2,3-d]pyrimidine-6-carboxamide)

Formula II compounds have a structure of Formula II, including pharmaceutically acceptable solvates (e.g., hydrates) thereof, and pharmaceutically acceptable salts thereof:

wherein:

each X is independently a heteroatom (e.g., O, S, and N); and

each R₁ is independently selected from the group consisting of hydrogen, lower alkyl, carboxy-lower alkyl, oxygen, and cycloalkyl.

Unless otherwise specified, a lower alkyl as used herein is an alkyl having 1, 2, 3, 4, 5, or 6 carbons.

Formula III compounds have a structure of Formula III, including pharmaceutically acceptable solvates (e.g., hydrates) thereof, and pharmaceutically acceptable salts thereof:

-   -   wherein:     -   R₂ is selected from the group consisting of hydrogen, halogen         atoms, NH₂, NHR₂, NHCOR₂, NO₂, CN, CH₂NH₂ CH₂NHR₂, phenyl and         heteroaromatic groups, wherein the phenyl or heteroaromatic         group is optionally substituted with a further substitution         selected from the group consisting of lower alkyl, carboxy-lower         alkyl, oxygen, and cycloalkyl groups;     -   Ar is phenyl or heteroaromatic group, wherein the phenyl or         heteroaromatic group is optionally substituted with a further         substitution selected from the group consisting of lower alkyl,         carboxy-lower alkyl (—(C═O)-lower alkyl), oxygen (═O), or         cycloalkyl groups; and     -   n is 0, 1, 2 or 3.

Formula IV compounds have a structure of Formula IV as disclosed in EP1295878B1, which is herein incorporated by reference, further including pharmaceutically acceptable solvates (e.g., hydrates) thereof, and pharmaceutically acceptable salts thereof:

wherein:

Ar₂ is

and Ar is or

Ar₂ is idem and Ar is

Combination Therapy

(1) Combination of RAD1901 or Solvates (e.g., Hydrate) or Salts Thereof and One or More CDK4 and/or CDK6 Inhibitor(s)

Both RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s), when administered alone to a subject, have a therapeutic effect on one or more cancers or tumors (Examples I(A) and I(B)). It was surprisingly discovered that when administered in combination to a subject, RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s) have a significantly improved effect on the cancers/tumors (Examples I(A) and I(B)).

“Inhibiting growth” of an ERα-positive tumor as used herein may refer to slowing the rate of tumor growth, or halting tumor growth entirely.

“Tumor regression” or “regression” of an ERα-positive tumor as used herein may refer to reducing the maximum size of a tumor. In certain embodiments, administration of a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof may result in a decrease in tumor size versus baseline (i.e., size prior to initiation of treatment), or even eradication or partial eradication of a tumor. Accordingly, in certain embodiments the methods of tumor regression provided herein may be alternatively characterized as methods of reducing tumor size versus baseline.

“Tumor” as used herein is a malignant tumor, and is used interchangeably with “cancer.”

Tumor growth inhibition or regression may be localized to a single tumor or to a set of tumors within a specific tissue or organ, or may be systemic (i.e., affecting tumors in all tissues or organs).

As RAD1901 is known to preferentially bind ERα versus estrogen receptor beta (ERβ), unless specified otherwise, estrogen receptor, estrogen receptor alpha, ERα, ER, wild-type ERα, and ESR1 are used interchangeably herein. “Estrogen receptor alpha” or “ERα” as used herein refers to a polypeptide comprising, consisting of, or consisting essentially of the wild-type ERα amino acid sequence, which is encoded by the gene ESR1. A tumor that is “positive for estrogen receptor alpha,” “ERα-positive,” “ER+,” or “ERα+” as used herein refers to a tumor in which one or more cells express at least one isoform of ERα. In certain embodiments, these cells overexpress ERα. In certain embodiments, the patient has one or more cells within the tumor expressing one or more forms of ERβ. In certain embodiments, the ERα-positive tumor and/or cancer is associated with breast, uterine, ovarian, or pituitary cancer. In certain of these embodiments, the patient has a tumor located in breast, uterine, ovarian, or pituitary tissue. In those embodiments where the patient has a tumor located in the breast, the tumor may be associated with luminal breast cancer that may or may not be positive for HER2, and for HER2+ tumors, the tumors may express high or low HER2 (e.g., FIG. 1). In other embodiments, the patient has a tumor located in another tissue or organ (e.g., bone, muscle, brain), but is nonetheless associated with breast, uterine, ovarian, or pituitary cancer (e.g., tumors derived from migration or metastasis of breast, uterine, ovarian, or pituitary cancer). Accordingly, in certain embodiments of the tumor growth inhibition or tumor regression methods provided herein, the tumor being targeted is a metastatic tumor and/or the tumor has an overexpression of ER in other organs (e.g., bones and/or muscles). In certain embodiments, the tumor being targeted is a brain tumor and/or cancer. In certain embodiments, the tumor being targeted is more sensitive to a treatment of RAD1901 and a CDK4 and/or CDK 6 inhibitor as disclosed herein than treatment with another SERD (e.g., fulvestrant, TAS-108 (SR16234), ZK191703, RU58668, GDC-0810 (ARN-810), GW5638/DPC974, SRN-927, ICI182782 and AZD9496), Her2 inhibitors (e.g., trastuzumab, lapatinib, ado-trastuzumab emtansine, and/or pertuzumab), chemo therapy (e.g., abraxane, adriamycin, carboplatin, cytoxan, daunorubicin, doxil, ellence, fluorouracil, gemzar, helaven, lxempra, methotrexate, mitomycin, micoxantrone, navelbine, taxol, taxotere, thiotepa, vincristine, and xeloda), aromatase inhibitor (e.g., anastrozole, exemestane, and letrozole), selective estrogen receptor modulators (e.g., tamoxifen, raloxifene, lasofoxifene, and/or toremifene), angiogenesis inhibitor (e.g., bevacizumab), and/or rituximab.

In certain embodiments of the tumor growth inhibition or tumor regression methods provided herein, the methods further comprise a step of determining whether a patient has a tumor expressing ERα prior to administering a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof. In certain embodiments of the tumor growth inhibition or tumor regression methods provided herein, the methods further comprise a step of determining whether the patient has a tumor expressing mutant ERα prior to administering a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof. In certain embodiments of the tumor growth inhibition or tumor regression methods provided herein, the methods further comprise a step of determining whether a patient has a tumor expressing ERα that is responsive or non-responsive to fulvestrant treatment prior to administering a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof. These determinations may be made using any method of expression detection known in the art, and may be performed in vitro using a tumor or tissue sample removed from the subject.

In addition to demonstrating the ability of RAD1901 to inhibit tumor growth in tumors expressing wild-type ERα, the results provided herein show that RAD1901 exhibited the unexpected ability to inhibit the growth of tumors expressing a mutant form of ERα, namely Y537S ERα (Example I(A)). Computer modeling evaluations of examples of ERα mutations showed that none of these mutations were expected to impact the LBD or specifically hinder RAD1901 binding (Example V(A)), e.g., ERα having one or more mutants selected from the group consisting of ERα with Y537X mutant wherein X is S, N, or C, ERα with D538G mutant, and ERα with S463P mutant. Based on these results, methods are provided herein for inhibiting growth or producing regression of a tumor that is positive for ERα having one or more mutants within the ligand-binding domain (LBD), selected from the group consisting of Y537X₁ wherein X₁ is S, N, or C, D538G, L536X₂ wherein X₂ is R or Q, P535H, V534E, S463P, V392I, E380Q, especially Y537S ERα, in a subject with cancer by administering to the subject a therapeutically effective amount of a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof. In certain embodiments, RAD1901 or solvates (e.g., hydrate) or salts thereof. “Mutant ERα” as used herein refers to ERα comprising one or more substitutions or deletions, and variants thereof comprising, consisting of, or consisting essentially of an amino acid sequence with at least 80%, at least 85%, at least 90%, at least 95%, at least 97%, at least 98%, at least 99%, or at least 99.5% identity to the amino acid sequence of ERα.

In addition to inhibiting breast cancer tumor growth in an animal xenograft model, the results disclosed herein show that RAD1901 exhibits significant accumulation within tumor cells, and is capable of penetrating the blood-brain barrier (Example II). The ability to penetrate the blood-brain barrier was confirmed by showing that RAD1901 administration significantly prolonged survival in a brain metastasis xenograft model (Example I(B)). Accordingly, in certain embodiments of the tumor growth inhibition or tumor regression methods provided herein, the ERα-positive tumor being targeted is located in the brain or elsewhere in the central nervous system. In certain of these embodiments, the ERα-positive tumor is primarily associated with brain cancer. In other embodiments, the ERα-positive tumor is a metastatic tumor that is primarily associated with another type of cancer, such as breast, uterine, ovarian, or pituitary cancer, or a tumor that has migrated from another tissue or organ. In certain of these embodiments, the tumor is a brain metastases, such as breast cancer brain metastases (BCBM). In certain embodiments of the methods disclosed herein, RAD1901 or solvates (e.g., hydrate) or salts thereof accumulate in one or more cells within a target tumor.

In certain embodiments of the methods disclosed herein, RAD1901 or solvates (e.g., hydrate) or salts thereof preferably accumulate in tumor at a T/P (RAD1901 concentration in tumor/RAD1901 concentration in plasma) ratio of about 15 or higher, about 18 or higher, about 19 or higher, about 20 or higher, about 25 or higher, about 28 or higher, about 30 or higher, about 33 or higher, about 35 or higher, or about 40 or higher.

The results provided herein show that RAD1901 administration protects against bone loss in ovariectomized rats (Example IV(A)). Accordingly, in certain embodiments of the tumor growth inhibition or tumor regression methods provided herein, administration of a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof does not have undesirable effects on bone, including for example undesirable effects on bone volume density, bone surface density, bone mineral density, trabecular number, trabecular thickness, trabecular spacing, connectivity density, and/or apparent bone density of the treated subject. As tamoxifen may be associated with bone loss in premenopausal women, and fulvestrant may impair the bone structures due to its mechanism of action, a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof can be particularly useful for premenopausal women, tumors resistant to tamoxifen or antiestrogen therapy, and patients having osteoporosis and/or high risk of osteoporosis.

The results provided herein show that RAD1901 antagonized estradiol stimulation of uterine tissues in ovariectomized rats (Example IV(A)). Furthermore, in human subjects treated with RAD1901 at a dosage of 200 mg or up to 500 mg q.d., standardized uptake value (SUV) for uterus, muscle, and bone tissues that did not significantly express ER showed hardly any changes in signals pre- and post-treatment (Example III(A)). Accordingly, in certain embodiments, such administration also does not result in undesirable effects on other tissues, including for example uterine, muscle, or breast tissue.

RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor (e.g., ribociclib, abemaciclib and palbociclib) disclosed herein are administered in combination to a subject in need. The phrase “in combination” means RAD1901 or solvates (e.g., hydrate) or salts thereof may be administered before, during, or after the administration of the CDK4 and/or CDK6 inhibitor. For example, RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor (e.g., ribociclib, abemaciclib and palbociclib) disclosed herein can be administered in about one week apart, about 6 days apart, about 5 days apart, about 4 days apart, about 3 days apart, about 2 days apart, about 24 hours apart, about 23 hours apart, about 22 hours apart, about 21 hours apart, about 20 hours apart, about 19 hours apart, about 18 hours apart, about 17 hours apart, about 16 hours apart, about 15 hours apart, about 14 hours apart, about 13 hours apart, about 12 hours apart, about 11 hours apart, about 10 hours apart, about 9 hours apart, about 8 hours apart, about 7 hours apart, about 6 hours apart, about 5 hours apart, about 4 hours apart, about 3 hours apart, about 2 hours apart, about 1 hour apart, about 55 minutes apart, about 50 minutes apart, about 45 minutes apart, about 40 minutes apart, about 35 minutes apart, about 30 minutes apart, about 25 minutes apart, about 20 minutes apart, about 15 minutes apart, about 10 minutes apart, or about 5 minutes apart. In other embodiments RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor (e.g., ribociclib, abemaciclib and palbociclib) disclosed herein are administered to the subject simultaneously or substantially simultaneously. In certain of these embodiments, RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor (e.g., ribociclib, abemaciclib and palbociclib) disclosed herein may be administered as part of a single formulation.

In some embodiments, the combination of RAD1901 or solvates (e.g., hydrate) or salts thereof and a single CDK4 and/or CDK6 inhibitor is administered to a subject. In other embodiments, the combination of RAD1901 or solvates (e.g., hydrate) or salts thereof and more than one CDK4 and/or CDK6 inhibitor is administered to a subject. For example, RAD1901 or solvates (e.g., hydrate) or salts thereof can be combined with two or more CDK4 and/or CDK6 inhibitors for treating cancers/tumors.

(2) Dosage

A therapeutically effective amount of a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof for use in the methods disclosed herein is an amount that, when administered over a particular time interval, results in achievement of one or more therapeutic benchmarks (e.g., slowing or halting of tumor growth, resulting in tumor regression, cessation of symptoms, etc.). The combination for use in the presently disclosed methods may be administered to a subject one time or multiple times. In those embodiments wherein the compounds are administered multiple times, they may be administered at a set interval, e.g., daily, every other day, weekly, or monthly. Alternatively, they can be administered at an irregular interval, for example on an as-needed basis based on symptoms, patient health, and the like. A therapeutically effective amount of the combination may be administered q.d. for one day, at least 2 days, at least 3 days, at least 4 days, at least 5 days, at least 6 days, at least 7 days, at least 10 days, or at least 15 days. Optionally, the status of the cancer or the regression of the tumor is monitored during or after the treatment, for example, by a FES-PET scan of the subject. The dosage of the combination administered to the subject can be increased or decreased depending on the status of the cancer or the regression of the tumor detected.

Ideally, the therapeutically effective amount does not exceed the maximum tolerated dosage at which 50% or more of treated subjects experience nausea or other toxicity reactions that prevent further drug administrations. A therapeutically effective amount may vary for a subject depending on a variety of factors, including variety and extent of the symptoms, sex, age, body weight, or general health of the subject, administration mode and salt or solvate type, variation in susceptibility to the drug, the specific type of the disease, and the like.

Examples of therapeutically effective amounts of a RAD1901 or solvates (e.g., hydrate) or salts thereof for use in the methods disclosed herein include, without limitation, about 150 to about 1,500 mg, about 200 to about 1,500 mg, about 250 to about 1,500 mg, or about 300 to about 1,500 mg dosage q.d. for subjects having resistant ER-driven tumors or cancers; about 150 to about 1,500 mg, about 200 to about 1,000 mg or about 250 to about 1,000 mg or about 300 to about 1,000 mg dosage q.d. for subjects having both wild-type ER driven tumors and/or cancers and resistant tumors and/or cancers; and about 300 to about 500 mg, about 300 to about 550 mg, about 300 to about 600 mg, about 250 to about 500 mg, about 250 to about 550 mg, about 250 to about 600 mg, about 200 to about 500 mg, about 200 to about 550 mg, about 200 to about 600 mg, about 150 to about 500 mg, about 150 to about 550 mg, or about 150 to about 600 mg q.d. dosage for subjects having majorly wild-type ER driven tumors and/or cancers. In certain embodiments, the dosage of a compound of Formula I (e.g., RAD1901) or a salt or solvate thereof for use in the presently disclosed methods general for an adult subject may be approximately 200 mg, 400 mg, 30 mg to 2,000 mg, 100 mg to 1,500 mg, or 150 mg to 1,500 mg p.o., q.d. This daily dosage may be achieved via a single administration or multiple administrations.

A therapeutically effective amount or dosage of a CDK4 and/or CDK6 inhibitor as described herein (e.g., ribociclib, abemaciclib and palbociclib) depends on its particular type. In general, the daily dosage of a CDK4 and/or CDK6 inhibitor as described herein (e.g., ribociclib, abemaciclib and palbociclib) ranges from about 1 mg to about 1,500 mg, from about 1 mg to about 1,200 mg, from about 1 mg to about 1,000 mg, from about 1 mg to about 800 mg, from about 1 mg to about 600 mg, from about 1 mg to about 500 mg, from about 1 mg to about 200 mg, from about 1 mg to about 100 mg, from about 1 mg to about 50 mg, from about 1 mg to about 30 mg, from about 1 mg to about 20 mg, from about 1 mg to about 10 mg, from about 1 mg to about 5 mg, from about 50 mg to about 1,500 mg, from about 100 mg to about 1,200 mg, from about 150 mg to about 1,000 mg, from about 200 mg to about 800 mg, from about 300 mg to about 600 mg, from about 350 mg to about 500 mg.

Abemaciclib

Dosing of RAD1901 with abemaciclib can be accomplished with RAD1901 at 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1,000 mg per day. In particular, 200 mg, 400 mg, 500 mg, 600 mg, 800 mg and 1,000 mg per day are noted. Under certain circumstances a BID dosing schedule is preferred. The surprisingly long half-life of RAD1901 in humans after PO dosing make this option particularly viable. Accordingly, the drug may be administered as 200 mg bid (400 mg total daily), 250 mg bid (500 mg total daily), 300 mg bid (600 mg total daily), 400 mg bid (800 mg daily) or 500 mg bid (1,000 mg total daily). Preferably the dosing is oral. The dose of abemaciclib may be 50 mg to 500 mg daily, or 150 mg to 450 mg daily and the dosing can be daily in 28 day cycles or less than 28 days per 28 day cycles such as 21 days per 28 day cycle or 14 days per 28 day cycle or 7 days per 28 day cycles. In some embodiments, the abemaciclib is dosed once daily or preferably on a bid schedule where dosing is oral. In the case of bid dosing, the doses can be separated by 4 hours, 8 hours or 12 hours. In certain embodiments, the abemaciclib is dosed at 150 mg bid via oral where the doses are recommended to be spaced out by 12 hours.

As has been discovered and explained herein, there appears to be a remarkable synergy between RAD1901 and cdk 4/6 inhibitors and therefore, a dose reduction of RAD 1901 and/or abemaciclib from the usual recommended or approved dose is contemplated and described herein. For example, RAD 1901 may be recommended for monotherapy treatment at doses of 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1,000 mg or more specifically at 200 mg, 400 mg, 500 mg, 600 mg, 800 mg and 1,000 mg per day. In combination, a reduction of the specified dose by a given fraction means that doses of 25% to 75% less than the usual dose are possible. BY way of non-limiting example, a recommended dose of RAD1901 of 400 mg per day may be reduced to between a final dose of 100 mg and 300 mg per day, or 100 mg per day, 200 mg per day or 300 mg per day. If the RAD1901 dose is reduced as described, the same percent reduction is generally applied whether the dosing is bid or once daily. For example, a 400 mg bid dose reduced by 50% would be administered on a 200 mg bid schedule. In some exceptions, a reduction of a daily recommended bid dose may be sufficient to allow for the total daily dose to be administered as a once daily dose. For example, a normal bid dose of 300 mg that is given in combination with abemaciclib may be reduced by 50%. Accordingly, the dose may be given as 150 mg bid or 300 mg once daily.

Similarly, the normal recommended dose of abemaciclib may be reduced when used in combination with RAD1901. The dose of abemaciclib may be reduced and combined with the normal recommended monotherapy dose of RAD1901 or a reduced RAD1901 dose wherein the reduced dose is 25% to 75% less than the normal recommended dose as exemplified immediately above. For example, a recommended dose of abemaciclib of 150 mg bid might be given as a bid dose of 25% to 75% less than the 150 mg bid dose. For example, 150 mg bid of abemaciclib may be reduced to a bid dose of 37.5 mg to 112.5 mg (total daily dose of 75 mg to 225 mg). Alternatively, it may be desirable to reduce the frequency of abemaciclib from a recommended 28 day on cycle to some amount less. For example, the dosing frequency can be reduced to 22 days to 27 days out of a 28 day cycle or to 21 days out of a 28 day cycle, or the dosing frequency may be reduced to 15 days to 20 days out of a 28 day cycle or to 14 days out of a 28 day cycle, or the dosing frequency may be reduced to 8 days to 13 days out of a 28 day cycle or to just 7 days out of a 28 day cycle. The days dosed may be consecutive or combined as needed under the circumstance. In one embodiment, the total dose over a dosing interval is reduced by 25% to 75% of the recommended dose and that reduction may come as a result of less frequent dosing, reduced dosage or a combination thereof. For example, a recommended dosing cycle of 28 days of abemaciclib at a dose of 150 mg bid (300 mg total daily) results in a total dose over 28 days of 8,400 mg (28 days times 300 mg total per day). This amount can be reduced to between from 2,100 mg per 28 day to 6,300 mg per 28 day.

Ribociclib

Dosing of RAD1901 with ribociclib can be accomplished with RAD1901 at 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1,000 mg per day. In particular, 200 mg, 400 mg, 500 mg, 600 mg, 800 mg and 1,000 mg per day are noted. Under certain circumstances a BID dosing schedule preferred. The surprisingly long half-life of RAD1901 in humans after PO dosing make this option particularly viable. Accordingly, the drug may be administered as 200 mg bid (400 mg total daily), 250 mg bid (500 mg total daily), 300 mg bid (600 mg total daily), 400 mg bid (800 mg daily) or 500 mg bid (1,000 mg total daily). Preferably the dosing is oral. The dose of ribociclib may be 200 mg to 1,000 mg daily, or 250 mg to 750 mg daily and the dosing can be daily in 28 day cycles or less than 28 days per 28 day cycles such as 21 days per 28 day cycle or 14 days per 28 day cycle or 7 days per 28 day cycles. In some embodiments, the ribociclib is dosed once daily where dosing is oral. In certain embodiments, the dose of ribociclib to be used in combination with RAD1901 is 600 mg once daily and the dosing interval is 21 days out of a 28 day cycle.

As has been discovered and explained herein, there appears to be a remarkable synergy between RAD1901 and cdk4/6 inhibitors and therefore, a dose reduction of RAD 1901 and/or ribociclib from the usual recommended or approved dose is contemplated and described herein. For example, RAD 1901 may be recommended for monotherapy treatment at doses of 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1,000 mg or more specifically at 200 mg, 400 mg, 500 mg, 600 mg, 800 mg and 1,000 mg per day. In combination, a reduction of the specified dose by a given fraction means that doses of 25% to 75% less than the usual dose are possible. BY way of non-limiting example, a recommended dose of RAD1901 of 400 mg per day may be reduced to between a final dose of 100 mg and 300 mg per day, or 100 mg per day, 200 mg per day or 300 mg per day. If the RAD1901 dose is reduced as described, the same percent reduction is generally applied whether the dosing is bid or once daily. For example, a 400 mg bid dose reduced by 50% would be administered on a 200 mg bid schedule. In some exceptions, a reduction of a daily recommended bid dose may be sufficient to allow for the total daily dose to be administered as a once daily dose. For example, a normal bid dose of 300 mg that is given in combination with ribociclib may be reduced by 50%. Accordingly, the dose may be given as 150 mg bid or 300 mg once daily.

Similarly, the normal recommended dose of ribociclib may be reduced when used in combination with RAD1901. The dose of ribociclib may be reduced and combined with the normal recommended monotherapy dose of RAD1901 or a reduced RAD1901 dose wherein the reduced dose is 25% to 75% less than the normal recommended dose as exemplified immediately above. For example, a recommended dose of ribociclib of 600 mg qd might be given as a qd dose of 25% to 75% less than the 600 mg dose. For example, 600 mg of a recommended ribociclib dose may be reduced to a dose of between 150 mg to 450 mg. Alternatively, it may be desirable to reduce the frequency of ribociclib from a recommended 21 day out of 28 day on cycle to some amount less. For example, the dosing frequency can be reduced to 15 to 20 days to out of a 28 day cycle or to 14 days out of a 28 day cycle, or the dosing frequency may be reduced to 8 days to 13 days out of a 28 day cycle or to 7 days out of a 28 day cycle. The days dosed may be consecutive or combined as needed under the circumstance. In one embodiment, the total dose over a dosing interval is reduced by 25% to 75% of the recommended dose and that reduction may come as a result of less frequent dosing, reduced dosage or a combination thereof. For example, a recommended dosing cycle of 28 days of ribociclib (21 days at a dose of 600 mg qd) results in a total dose over 28 days of 12,600 mg (21 dosing days times 600 mg total per day). This amount can be reduced to between from 3,150 mg per 28 day cycle to 9,450 mg per 28 day cycle.

Palbociclib

Dosing of RAD1901 with palbociclib can be accomplished with RAD1901 at 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1,000 mg per day. In particular, 200 mg, 400 mg, 500 mg, 600 mg, 800 mg and 1,000 mg per day are noted. Under certain circumstances a BID dosing schedule preferred. The surprisingly long half-life of RAD1901 in humans after PO dosing make this option particularly viable. Accordingly, the drug may be administered as 200 mg bid (400 mg total daily), 250 mg bid (500 mg total daily), 300 mg bid (600 mg total daily), 400 mg bid (800 mg daily) or 500 mg bid (1,000 mg total daily). Preferably the dosing is oral. The dose of palbociclib may be 25 mg to 250 mg daily, or 50 mg to 125 mg daily or from 75 mg to 125 mg daily or 75 mg daily or 100 mg daily or 125 mg daily. The dosing can be daily in 28 day cycles or less than 28 days per 28 day cycles such as 21 days per 28 day cycle or 14 days per 28 day cycle or 7 days per 28 day cycles. In some embodiments, the palbociclib is dosed once daily where dosing is oral. In certain embodiments, the dose of palbociclib to be used in combination with RAD1901 is 125 mg once daily and the dosing interval is 21 days out of a 28 day cycle, or 100 mg once daily and the dosing interval is 21 days out of a 28 day cycle or 75 mg once daily and the dosing interval is 21 days out of a 28 day cycle.

As has been discovered and explained herein, there appears to be a remarkable synergy between RAD1901 and palbociclib and therefore, a dose reduction of RAD 1901 and/or palbociclib from the usual recommended or approved dose is contemplated and described herein. For example, RAD 1901 may be recommended for monotherapy treatment at doses of 100, 200, 300, 400, 500, 600, 700, 800, 900 or 1,000 mg or more specifically at 200 mg, 400 mg, 500 mg, 600 mg, 800 mg and 1,000 mg per day. In combination, a reduction of the specified dose by a given fraction means that doses of 25% to 75% less than the usual dose are possible. BY way of non-limiting example, a recommended dose of RAD1901 of 400 mg per day may be reduced to between a final dose of 100 mg and 300 mg per day, or 100 mg per day, 200 mg per day or 300 mg per day. If the RAD1901 dose is reduced as described, the same percent reduction is generally applied whether the dosing is bid or once daily. For example, a 400 mg bid dose reduced by 50% would be administered on a 200 mg bid schedule. In some exceptions, a reduction of a daily recommended bid dose may be sufficient to allow for the total daily dose to be administered as a once daily dose. For example, a normal bid dose of 300 mg that is given in combination with palbociclib may be reduced by 50%. Accordingly, the dose may be given as 150 mg bid or 300 mg once daily.

Similarly, the normal recommended dose of palbociclib may be reduced when used in combination with RAD1901. The dose of palbociclib may be reduced and combined with the normal recommended monotherapy dose of RAD1901 or a reduced RAD1901 dose wherein the reduced dose is 25% to 75% less than the normal recommended dose as exemplified immediately above. For example, a recommended dose of palbociclib of 125 mg qd might be given as a qd dose of 25% to 75% less than the 125 mg dose. For example, 125 mg of a recommended palbociclib dose may be reduced to a dose of between 31.25 mg to 93.75 mg. In some embodiments, a specific pre-specified reduction dose of from 125 mg to 100 mg daily or from 125 mg to 75 mg daily may be used. Alternatively, it may be desirable to reduce the frequency of palbociclib from a recommended 21 day out of 28 day on cycle to some amount less. For example, the dosing frequency can be reduced to 15 to 20 days to out of a 28 day cycle or to 14 days out of a 28 day cycle, or the dosing frequency may be reduced to 8 days to 13 days out of a 28 day cycle or to 7 days out of a 28 day cycle. The days dosed may be consecutive or combined as needed under the circumstance. In one embodiment, the total dose over a dosing interval is reduced by 25% to 75% of the recommended dose and that reduction may come as a result of less frequent dosing, reduced dosage or a combination thereof. For example, a recommended dosing cycle of 28 days of palbociclib (21 days at a dose of 125 mg qd) results in a total dose over 28 days of 2,625 mg (21 dosing days times 125 mg total per day). This amount can be reduced to between from 656.25 mg per 28 day cycle to 1,968.75 mg per 28 day cycle. In another embodiment, a recommended 28 day total cycle dose of 2,625 mg be reduced to 2,100 mg per 28 day cycle.

In certain embodiments, a therapeutically effective amount of the combination may utilize a therapeutically effective amount of either compound administered alone. In other embodiments, due to the significantly improved, synergistic therapeutic effect achieved by the combination, the therapeutically effective amounts of RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) when administered in the combination may be smaller than the therapeutically effective amounts of RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) required when administered alone; and one or both compounds may be administered at a dosage that is lower than the dosage at which they would normally be administered when given separately. Without being bound by any specific theory, the combination therapy achieves a significantly improved effect by reducing the dosage of at least one or all of RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib), thereby eliminating or alleviating undesirable toxic side effects.

In some embodiments, the therapeutically effective amount of RAD1901 or solvates (e.g., hydrate) or salts thereof when administered as part of the combination is about 30% to about 200%, about 40% to about 200%, about 50% to about 200%, about 60% to about 200%, about 70% to about 200%, about 80% to about 200%, about 90% to about 200%, about 100% to about 200%, 30% to about 150%, about 40% to about 150%, about 50% to about 150%, about 60% to about 150%, about 70% to about 150%, about 80% to about 150%, about 90% to about 150%, about 100% to about 150%, about 30% to about 120%, about 40% to about 120%, about 50% to about 120%, about 60% to about 120%, about 70% to about 120%, about 80% to about 120%, about 90% to about 120%, about 100% to about 120%, 30% to about 110%, about 40% to about 110%, about 50% to about 110%, about 60% to about 110%, about 70% to about 110%, about 80% to about 110%, about 90% to about 110%, or about 100% to about 110% of the therapeutically effective amount of RAD1901 or solvates (e.g., hydrate) or salts thereof when administered alone. In some embodiments, the therapeutically effective amount of the CDK4 and/or CDK6 inhibitor as described herein (e.g., ribociclib, abemaciclib and palbociclib) when administered as part of the combination is about 30% to about 200%, about 40% to about 200%, about 50% to about 200%, about 60% to about 200%, about 70% to about 200%, about 80% to about 200%, about 90% to about 200%, about 100% to about 200%, 30% to about 150%, about 40% to about 150%, about 50% to about 150%, about 60% to about 150%, about 70% to about 150%, about 80% to about 150%, about 90% to about 150%, about 100% to about 150%, about 30% to about 120%, about 40% to about 120%, about 50% to about 120%, about 60% to about 120%, about 70% to about 120%, about 80% to about 120%, about 90% to about 120%, about 100% to about 120%, 30% to about 110%, about 40% to about 110%, about 50% to about 110%, about 60% to about 110%, about 70% to about 110%, about 80% to about 110%, about 90% to about 110%, or about 100% to about 110% of the therapeutically effective amount of the CDK4 and/or CDK6 inhibitor as described herein (e.g., ribociclib, abemaciclib and palbociclib) when administered alone.

In certain embodiments, the cancers or tumors are resistant ER-driven cancers or tumors (e.g. having mutant ER binding domains (e.g. ERα comprising one or more mutations including, but not limited to, Y537X₁ wherein X₁ is S, N, or C, D538G, L536X₂ wherein X₂ is R or Q, P535H, V534E, S463P, V392I, E380Q and combinations thereof), overexpressors of the ERs or tumor and/or cancer proliferation becomes ligand independent, or tumors and/or cancers that progress with treatment of another SERD (e.g., fulvestrant, TAS-108 (SR16234), ZK191703, RU58668, GDC-0810 (ARN-810), GW5638/DPC974, SRN-927, ICI182782 and AZD9496), Her2 inhibitors (e.g., trastuzumab, lapatinib, ado-trastuzumab emtansine, and/or pertuzumab), chemo therapy (e.g., abraxane, adriamycin, carboplatin, cytoxan, daunorubicin, doxil, ellence, fluorouracil, gemzar, helaven, lxempra, methotrexate, mitomycin, micoxantrone, navelbine, taxol, taxotere, thiotepa, vincristine, and xeloda), aromatase inhibitor (e.g., anastrozole, exemestane, and letrozole), selective estrogen receptor modulators (e.g., tamoxifen, raloxifene, lasofoxifene, and/or toremifene), angiogenesis inhibitor (e.g., bevacizumab), and/or rituximab.

In certain embodiments, the dosage of RAD1901 or solvates (e.g., hydrate) or salts thereof in a combination with a CDK4 and/or CDK6 inhibitor as described herein (e.g., ribociclib, abemaciclib and palbociclib) for use in the presently disclosed methods general for an adult subject may be approximately 30 mg to 2,000 mg, 100 mg to 1,500 mg, or 150 mg to 1,500 mg p.o., q.d. This daily dosage may be achieved via a single administration or multiple administrations.

A combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof may be administered to a subject one time or multiple times. In those embodiments wherein the compounds are administered multiple times, they may be administered at a set interval, e.g., daily, every other day, weekly, or monthly. Alternatively, they can be administered at an irregular interval, for example on an as-needed basis based on symptoms, patient health, and the like.

(3) Formulation

In some embodiments, RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) are administered in separate formulations. In certain of these embodiments, the formulations may be of the same type. For example, both formulations may be designed for oral administration (e.g., via two separate pills) or for injection (e.g., via two separate injectable formulations). In other embodiments, RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) may be formulated in different types of formulations. For example, one compound may be in a formulation designed for oral administration, while the other is in a formulation designed for injection.

In other embodiments, RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s) (e.g., ribociclib, abemaciclib and palbociclib) described herein are administered as part of a single formulation. For example, RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) are formulated in a single pill for oral administration or in a single dose for injection. Provided herein in certain embodiments are combination formulations comprising RAD1901 or solvates (e.g., hydrate) or salts thereof and one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib). In certain embodiments, administration of the compounds in a single formulation improves patient compliance.

The therapeutically effective amount of each compound when administered in combination may be lower than the therapeutically effective amount of each compound administered alone.

In some embodiments, a formulation comprising RAD1901 or solvates (e.g., hydrate) or salts thereof, one or more to the CDK4 and/or CDK6 inhibitor(s) (e.g., ribociclib, abemaciclib and palbociclib), or both RAD1901 or solvates (e.g., hydrate) or salts thereof and the one or more CDK4 and/or CDK6 inhibitor(s) (e.g., ribociclib, abemaciclib and palbociclib) may further comprise one or more pharmaceutical excipients, carriers, adjuvants, and/or preservatives.

The RAD1901 or solvates (e.g., hydrate) or salts thereof and the CDK4 and/or CDK6 inhibitor(s) (e.g., ribociclib, abemaciclib and palbociclib) for use in the presently disclosed methods can be formulated into unit dosage forms, meaning physically discrete units suitable as unitary dosage for subjects undergoing treatment, with each unit containing a predetermined quantity of active material calculated to produce the desired therapeutic effect, optionally in association with a suitable pharmaceutical carrier. The unit dosage form can be for a single daily dose or one of multiple daily doses (e.g., about 1 to 4 or more times q.d.). When multiple daily doses are used, the unit dosage form can be the same or different for each dose. In certain embodiments, the compounds may be formulated for controlled release.

The RAD1901 or solvates (e.g., hydrate) or salts thereof and salts or solvates and the CDK4 and/or CDK6 inhibitor(s) (e.g., ribociclib, abemaciclib and palbociclib) for use in the presently disclosed methods can be formulated according to any available conventional method. Examples of preferred dosage forms include a tablet, a powder, a subtle granule, a granule, a coated tablet, a capsule, a syrup, a troche, an inhalant, a suppository, an injectable, an ointment, an ophthalmic ointment, an eye drop, a nasal drop, an ear drop, a cataplasm, a lotion and the like. In the formulation, generally used additives such as a diluent, a binder, an disintegrant, a lubricant, a colorant, a flavoring agent, and if necessary, a stabilizer, an emulsifier, an absorption enhancer, a surfactant, a pH adjuster, an antiseptic, an antioxidant and the like can be used. In addition, the formulation is also carried out by combining compositions that are generally used as a raw material for pharmaceutical formulation, according to the conventional methods. Examples of these compositions include, for example, (1) an oil such as a soybean oil, a beef tallow and synthetic glyceride; (2) hydrocarbon such as liquid paraffin, squalane and solid paraffin; (3) ester oil such as octyldodecyl myristic acid and isopropyl myristic acid; (4) higher alcohol such as cetostearyl alcohol and behenyl alcohol; (5) a silicon resin; (6) a silicon oil; (7) a surfactant such as polyoxyethylene fatty acid ester, sorbitan fatty acid ester, glycerin fatty acid ester, polyoxyethylene sorbitan fatty acid ester, a solid polyoxyethylene castor oil and polyoxyethylene polyoxypropylene block co-polymer; (8) water soluble macromolecule such as hydroxyethyl cellulose, polyacrylic acid, carboxyvinyl polymer, polyethyleneglycol, polyvinylpyrrolidone and methylcellulose; (9) lower alcohol such as ethanol and isopropanol; (10) multivalent alcohol such as glycerin, propyleneglycol, dipropyleneglycol and sorbitol; (11) a sugar such as glucose and cane sugar; (12) an inorganic powder such as anhydrous silicic acid, aluminum magnesium silicicate and aluminum silicate; (13) purified water, and the like. Additives for use in the above formulations may include, for example, 1) lactose, corn starch, sucrose, glucose, mannitol, sorbitol, crystalline cellulose and silicon dioxide as the diluent; 2) polyvinyl alcohol, polyvinyl ether, methyl cellulose, ethyl cellulose, gum arabic, tragacanth, gelatine, shellac, hydroxypropyl cellulose, hydroxypropylmethyl cellulose, polyvinylpyrrolidone, polypropylene glycol-poly oxyethylene-block co-polymer, meglumine, calcium citrate, dextrin, pectin and the like as the binder; 3) starch, agar, gelatine powder, crystalline cellulose, calcium carbonate, sodium bicarbonate, calcium citrate, dextrin, pectic, carboxymethylcellulose/calcium and the like as the disintegrant; 4) magnesium stearate, talc, polyethyleneglycol, silica, condensed plant oil and the like as the lubricant; 5) any colorants whose addition is pharmaceutically acceptable is adequate as the colorant; 6) cocoa powder, menthol, aromatizer, peppermint oil, cinnamon powder as the flavoring agent; 7) antioxidants whose addition is pharmaceutically accepted such as ascorbic acid or alpha-tophenol.

The one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof for use in the presently disclosed methods can be formulated into a pharmaceutical composition as any one or more of the active compounds described herein and a physiologically acceptable carrier (also referred to as a pharmaceutically acceptable carrier or solution or diluent). Such carriers and solutions include pharmaceutically acceptable salts and solvates of compounds used in the methods of the instant invention, and mixtures comprising two or more of such compounds, pharmaceutically acceptable salts of the compounds and pharmaceutically acceptable solvates of the compounds. Such compositions are prepared in accordance with acceptable pharmaceutical procedures such as described in Remington's Pharmaceutical Sciences, 17th edition, ed. Alfonso R. Gennaro, Mack Publishing Company, Eaton, Pa. (1985), which is incorporated herein by reference.

The term “pharmaceutically acceptable carrier” refers to a carrier that does not cause an allergic reaction or other untoward effect in patients to whom it is administered and are compatible with the other ingredients in the formulation. Pharmaceutically acceptable carriers include, for example, pharmaceutical diluents, excipients or carriers suitably selected with respect to the intended form of administration, and consistent with conventional pharmaceutical practices. For example, solid carriers/diluents include, but are not limited to, a gum, a starch (e.g., corn starch, pregelatinized starch), a sugar (e.g., lactose, mannitol, sucrose, dextrose), a cellulosic material (e.g., microcrystalline cellulose), an acrylate (e.g., polymethylacrylate), calcium carbonate, magnesium oxide, talc, or mixtures thereof. Pharmaceutically acceptable carriers may further comprise minor amounts of auxiliary substances such as wetting or emulsifying agents, preservatives or buffers, which enhance the shelf life or effectiveness of the therapeutic agent.

The one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof in a free form can be converted into a salt by conventional methods. The term “salt” used herein is not limited as long as the salt is formed with RAD1901 or solvates (e.g., hydrate) or salts thereof and is pharmacologically acceptable; preferred examples of salts include a hydrohalide salt (for instance, hydrochloride, hydrobromide, hydroiodide and the like), an inorganic acid salt (for instance, sulfate, nitrate, perchlorate, phosphate, carbonate, bicarbonate and the like), an organic carboxylate salt (for instance, acetate salt, maleate salt, tartrate salt, fumarate salt, citrate salt and the like), an organic sulfonate salt (for instance, methanesulfonate salt, ethanesulfonate salt, benzenesulfonate salt, toluenesulfonate salt, camphorsulfonate salt and the like), an amino acid salt (for instance, aspartate salt, glutamate salt and the like), a quaternary ammonium salt, an alkaline metal salt (for instance, sodium salt, potassium salt and the like), an alkaline earth metal salt (magnesium salt, calcium salt and the like) and the like. In addition, hydrochloride salt, sulfate salt, methanesulfonate salt, acetate salt and the like are preferred as “pharmacologically acceptable salt” of the compounds according to the present invention.

Isomers of RAD1901 or solvates (e.g., hydrate) or salts thereof and/or the CDK4 and/or CDK6 inhibitor(s) (e.g., ribociclib, abemaciclib and palbociclib) disclosed herein (e.g., geometric isomers, optical isomers, rotamers, tautomers, and the like) can be purified using general separation means, including for example recrystallization, optical resolution such as diastereomeric salt method, enzyme fractionation method, various chromatographies (for instance, thin layer chromatography, column chromatography, glass chromatography and the like) into a single isomer. The term “a single isomer” herein includes not only an isomer having a purity of 100%, but also an isomer containing an isomer other than the target, which exists even through the conventional purification operation. A crystal polymorph sometimes exists for RAD1901 or solvates (e.g., hydrate) or salts thereof and/or a CDK4 and/or CDK6 inhibitor (e.g., ribociclib, abemaciclib and palbociclib), and all crystal polymorphs thereof are included in the present invention. The crystal polymorph is sometimes single and sometimes a mixture, and both are included herein.

In certain embodiments, RAD1901 or solvates (e.g., hydrate) or salts thereof and/or CDK4 and/or CDK6 inhibitor (e.g., ribociclib, abemaciclib and palbociclib) may be in a prodrug form, meaning that it must undergo some alteration (e.g., oxidation or hydrolysis) to achieve its active form. Alternative, RAD1901 or solvates (e.g., hydrate) or salts thereof and/or CDK4 and/or CDK6 inhibitor (e.g., ribociclib, abemaciclib and palbociclib) may be a compound generated by alteration of a parental prodrug to its active form.

(4) Administration Route

Administration routes of RAD1901 or solvates (e.g., hydrate) or salts thereof and/or CDK4 and/or CDK6 inhibitor(s) (e.g., ribociclib, abemaciclib and palbociclib) disclosed herein include but not limited to topical administration, oral administration, intradermal administration, intramuscular administration, intraperitoneal administration, intravenous administration, intravesical infusion, subcutaneous administration, transdermal administration, and transmucosal administration.

(5) Gene Profiling

In certain embodiments, the methods of tumor growth inhibition or tumor regression provided herein further comprise gene profiling the subject, wherein the gene to be profiled is one or more genes selected from the group consisting of ABL1, AKT1, AKT2, ALK, APC, AR, ARID 1A, ASXL1, ATM, AURKA, BAP, BAP1, BCL2L11, BCR, BRAF, BRCA1, BRCA2, CCND1, CCND2, CCND3, CCNE1, CDH1, CDK4, CDK6, CDK8, CDKN1A, CDKN1B, CDKN2A, CDKN2B, CEBPA, CTNNB1, DDR2, DNMT3A, E2F3, EGFR, EML4, EPHB2, ERBB2, ERBB3, ESR1, EWSR1, FBXW7, FGF4, FGFR1, FGFR2, FGFR3, FLT3, FRS2, HIF1A, HRAS, IDH1, IDH2, IGF1R, JAK2, KDM6A, KDR, KIF5B, KIT, KRAS, LRP1B, MAP2K1, MAP2K4, MCL1, MDM2, MDM4, MET, MGMT, MLL, MPL, MSH6, MTOR, MYC, NF1, NF2, NKX2-1, NOTCH1, NPM, NRAS, PDGFRA, PIK3CA, PIK3R1, PML, PTEN, PTPRD, RARA, RB1, RET, RICTOR, ROS1, RPTOR, RUNX1, SMAD4, SMARCA4, SOX2, STK11, TET2, TP53, TSC1, TSC2, and VHL.

In some embodiments, this invention provides a method of treating a subpopulation of breast cancer patients wherein said sub-population has increased expression of one or more of the genes disclosed supra, and treating said sub-population with an effective dose of a combination of one or more CDK4 and/or CDK6 inhibitor(s) as described herein (e.g., ribociclib, abemaciclib and palbociclib) and RAD1901 or solvates (e.g., hydrate) or salts thereof according to the dosing embodiments as described in this disclosure.

(6) Dose Adjusting

In addition to establishing the ability of RAD1901 to inhibit tumor growth, the results provided herein show that RAD1901 inhibits estradiol binding to ER in the uterus and pituitary (Example III(A)). In these experiments, estradiol binding to ER in uterine and pituitary tissue was evaluated by FES-PET imaging. After treatment with RAD1901, the observed level of ER binding was at or below background levels. These results establish that the antagonistic effect of RAD1901 on ER activity can be evaluated using real-time scanning. Based on these results, methods are provided herein for monitoring the efficacy of treatment RAD1901 or solvates (e.g., hydrate) or salts thereof in a combination therapy disclosed herein by measuring estradiol-ER binding in one or more target tissues, wherein a decrease or disappearance in binding indicates efficacy.

Further provided are methods of adjusting the dosage of RAD1901 or solvates (e.g., hydrate) or salts thereof in a combination therapy disclosed herein based on estradiol-ER binding. In certain embodiments of these methods, binding is measured at some point following one or more administrations of a first dosage of the compound. If estradiol-ER binding is not affected or exhibits a decrease below a predetermined threshold (e.g., a decrease in binding versus baseline of less than 5%, less than 10%, less than 20%, less than 30%, or less than 50%), the first dosage is deemed to be too low. In certain embodiments, these methods comprise an additional step of administering an increased second dosage of the compound. These steps can be repeated, with dosage repeatedly increased until the desired reduction in estradiol-ER binding is achieved. In certain embodiments, these steps can be incorporated into the methods of inhibiting tumor growth provided herein. In these methods, estradiol-ER binding can serve as a proxy for tumor growth inhibition, or a supplemental means of evaluating growth inhibition. In other embodiments, these methods can be used in conjunction with the administration of RAD1901 or solvates (e.g., hydrate) or salts thereof for purposes other than inhibition of tumor growth, including for example inhibition of cancer cell proliferation.

In certain embodiments, the methods provided herein for adjusting the dosage of RAD1901 or salt or solvate (e.g., hydrate) thereof in a combination therapy comprise:

-   -   (1) administering a first dosage of RAD1901 or salt or solvate         (e.g., hydrate) thereof (e.g., about 350 to about 500 or about         200 to about 600 mg/day) for 3, 4, 5, 6, or 7 days;     -   (2) detecting estradiol-ER binding activity, for example using         FES-PET imaging as disclosed herein; wherein:         -   (i) if the ER binding activity is not detectable or is below             a predetermined threshold level, continuing to administer             the first dosage (i.e., maintain the dosage level); or         -   (ii) if the ER binding activity is detectable or is above a             predetermined threshold level, administering a second dosage             that is greater than the first dosage (e.g., the first             dosage plus about 50 to about 200 mg) for 3, 4, 5, 6, or 7             days, then proceeding to step (3);     -   (3) detecting estradiol-ER binding activity, for example using         FES-PET imaging as disclosed herein; wherein         -   (i) if the ER binding activity is not detectable or is below             a predetermined threshold level, continuing to administer             the second dosage (i.e., maintain the dosage level); or         -   (ii) if the ER binding activity is detectable or is above a             predetermined threshold level, administering a third dosage             that is greater than the second dosage (e.g., the second             dosage plus about 50 to about 200 mg) for 3, 4, 5, 6, or 7             days, then proceeding to step (4);     -   (4) repeating the steps above through a fourth dosage, fifth         dosage, etc., until no ER binding activity is detected.

In certain embodiments, the invention includes the use of PET imaging to detect and/or dose ER sensitive or ER resistant cancers.

(7) Combinations for the Methods Disclosed Herein

Another aspect of the invention relates to a pharmaceutical composition comprising RAD1901 or solvates (e.g., hydrate) or salts thereof and/or CDK4 and/or CDK6 inhibitor(s) (e.g., ribociclib, abemaciclib and palbociclib) disclosed herein in a therapeutically effective amount as disclosed herein for the combination methods set forth herein.

RAD1901-ERα Interactions

(1) Mutant ERα in ER Positive Breast Tumor Samples from Patients Who Received at Least One Line of Endocrine Treatment

In five studies reported in the past two years, a total of 187 metastatic ER positive breast tumor samples from patients who received at least one line of endocrine treatment were sequenced and ER LBD mutations were identified in 39 patients (21%) (Jeselsohn). Among the 39 patients, the six most frequent LBD mutations are shown in FIG. 39 adapted from Jeselsohn.

The frequency of all LBD mutations are summarized in Table 9.

Computer modeling showed that RAD1901-ERα interactions are not likely to be affected by mutants of LBD of ERα, e.g., Y537X mutant wherein X was S, N, or C; D538G; and S463P, which account for about 81.7% of LBD mutations found in a recent study of metastatic ER positive breast tumor samples from patients who received at least one line of endocrine treatment (Table 10, Example V).

Provided herein are complexes and crystals of RAD1901 bound to ERα and/or a mutant ERα, the mutant ERα comprises one or more mutations including, but not limited to, Y537X₁ wherein X₁ is S, N, or C, D538G, L536X₂ wherein X₂ is R or Q, P535H, V534E, S463P, V392I, E380Q and combinations thereof.

In certain embodiments of the methods provided herein, the LBD of ERα and a mutant ERα comprises AF-2. In other embodiments, the LBD comprises, consists of, or consists essentially of amino acids 299-554 of ERα. In certain embodiments, the LBD of the mutant ERα comprises one or more mutations including, but not limited to, Y537X₁ wherein X₁ is S, N, or C, D538G, L536X₂ wherein X₂ is R or Q, P535H, V534E, S463P, V392I, E380Q and combinations thereof. The term “and/or” as used herein includes both the “and” case and the “or” case.

The following examples are provided to better illustrate the claimed invention and are not to be interpreted as limiting the scope of the invention. To the extent that specific materials are mentioned, it is merely for purposes of illustration and is not intended to limit the invention. One skilled in the art may develop equivalent means or reactants without the exercise of inventive capacity and without departing from the scope of the invention. It will be understood that many variations can be made in the procedures herein described while still remaining within the bounds of the present invention. It is the intention of the inventors that such variations are included within the scope of the invention.

EXAMPLES Materials and Methods Test Compounds

RAD1901 used in the examples below was (6R)-6-(2-(N-(4-(2-(ethylamino)ethyl)benzyl)-N-ethylamino)-4-methoxyphenyl)-5,6,7,8-tetrahydronaphthalen-2-ol dihydrochloride, manufactured by IRIX Pharmaceuticals, Inc. (Florence, S.C.). RAD1901 was stored as a dry powder, formulated for use as a homogenous suspension in 0.5% (w/v) methylcellulose in deionized water, and for animal models was administered p.o. Tamoxifen, raloxifene and estradiol (E2) were obtained from Sigma-Aldrich (St. Louis, Mo.), and administered by subcutaneous injection. Fulvestrant was obtained from Tocris Biosciences (Minneapolis, Minn.) and administered by subcutaneous injection. Other laboratory reagents were purchased from Sigma-Aldrich unless otherwise noted.

Cell Lines

MCF-7 cells (human mammary metastatic adenocarcinoma) were purchased from American Type Culture Collection (Rockville, Md.) and were routinely maintained in phenol red-free minimal essential medium (MEM) containing 2 mM L-glutamine and Earle's BSS, 0.1 mM non-essential amino acids and 1 mM sodium pyruvate supplemented with 0.01 mg/ml bovine insulin and 10% fetal bovine serum (Invitrogen, Carlsbad, Calif.), at 5% CO₂.

T47D cells were cultured in 5% CO₂ incubator in 10 cm dishes to approximately 75% confluence in RPMI growth media supplemented with 10% FBS and 5 μg/mL human insulin.

In Vivo Xenograft Models

All mice were housed in pathogen-free housing in individually ventilated cages with sterilized and dust-free bedding cobs, access to sterilized food and water ad libitum, under a light dark cycle (12-14 hour circadian cycle of artificial light) and controlled room temperature and humidity. Tumors were measured twice weekly with Vernier calipers and volumes were calculated using the formula: (L*W²)*0.52.

PDx Models

Some examples of patient-derived xenograft models (PDx models) are shown in FIG. 1. PDx models with patient derived breast cancer tumor were established from viable human tumor tissue or fluid that had been serially passaged in animals (athymic nude mice (Nu (NCF)-Foxn1 nu)) a limited number of times to maintain tumor heterogeneity. Pre-study tumor volumes were recorded for each experiment beginning approximately one week prior to its estimated start date. When tumors reached the appropriate Tumor Volume Initiation (TVI) range (150-250 mm³), animals were randomized into treatment and control groups and dosing initiated (Day 0, 8-10 subjects in each group); animals in all studies followed individually throughout each experiment. Initial dosing began Day 0; animals in all groups were dosed by weight (0.01 mL per gram; 10 ml/kg). Each group was treated with vehicle (control, p.o., q.d. to the endpoint), tamoxifen (1 mg/subject, s.c., q.o.d. to the end point), fulvestrant (Faslodex®; 1 mg/subject or 3 mg/subject as needed, s.c., qwk, ×5 and extended if necessary), or RAD1901 (30, 60 or 120 mg/kg of the subject, p.o., q.d. to the endpoint) as specified from day 0. The treatment period lasted for 56-60 days depending on the models. The drinking water for these PDx models was supplemented with 17β-estradiol.

Agent Efficacy

For all studies, beginning Day 0, tumor dimensions were measured by digital caliper and data including individual and mean estimated tumor volumes (Mean TV±SEM) recorded for each group; tumor volume was calculated using the formula (Yasui et al. Invasion Metastasis 17:259-269 (1997), which is incorporated herein by reference): TV=width²×length×0.52. Each group or study was ended once the estimated group mean tumor volume reached the Tumor Volume (TV) endpoint (time endpoint was 60 days; and volume endpoint was group mean 2 cm³); individual mice reaching a tumor volume of 2 cm³ or more were removed from the study and the final measurement included in the group mean until the mean reached volume endpoint or the study reached time endpoint.

Efficacy Calculations and Statistical Analysis

% Tumor Growth Inhibition (% TGI) values were calculated at a single time point (when the control group reached tumor volume or time endpoint) and reported for each treatment group (T) versus control (C) using initial (i) and final (f) tumor measurements by the formula (Corbett T H et al. In vivo methods for screening and preclinical testing. In: Teicher B, ed., Anticancer Drug Development Guide. Totowa, N.J.: Humana. 2004: 99-123.): % TGI=1−Tf−Ti/Cf−Ci.

Statistics

TGI Studies—One way ANOVA+Dunnett's Multiple Comparisons Test (Corbett T H et al).

Sample Collection

At endpoint, tumors were removed. One fragment was flash frozen, while another fragment was placed in 10% NBF for at least 24 hours and formalin fixed paraffin embedded (FFPE). Flash frozen samples were stored at −80° C.; FFPE blocks were stored at room temperature.

Western Blot

Cells were harvested and protein expression was analyzed using standard practice. Tumors were harvested at the indicated time points after the last day of dosing, homogenized in RIPA buffer with protease and phosphatase inhibitors using a Tissuelyser (Qiagen). Equal amounts of protein were separated by MW, transferred to nitrocellulose membranes and blotted with the following antibodies using standard practice:

-   -   Estrogen receptor (SantaCruz (HC-20); sc-543)     -   Progesterone receptor (Cell Signaling Technologies; 3153)     -   Vinculin (Sigma-Aldrich, v9131)

qPCR analyses were performed as follows: Cells were harvested, mRNA was extracted, and equal amounts used for cDNA synthesis and qPCR with primers specific for progesterone receptor, GREB1, and TFF1 (LifeTech). Bands were quantified using 1D Quant software (GE).

Immunohistochemistry

Tumors were harvested, formalin-fixed and embedded into paraffin. Embedded tumors were sectioned (6μ1\4) and stained with antibodies specific for ER, PR, and Her2. Quantitation was performed as follows: Five fields were counted for positive cells (0-100%) and intensity of staining (0-3+). H-scores (0-300) were calculated using the following formula: % positivity*intensity.

Example I. RAD1901-Palbo Combinations Provided Enhanced Tumor Growth Inhibition in Tumor and/or Cancer Expressing WT ER or Mutant ER (e.g., Y5378), with Different Prior Endocrine Therapy

I(A). Effectiveness of RAD1901 on Animal Xenografts Models

I(A)(i) RAD1901-Palbo Combinations Demonstrated Improved Tumor Growth Inhibition in PDx Models (PDx-1 to PDx-12) Regardless of ER Status and Prior Endocrine Therapy

FIG. 1 demonstrates tumor growth inhibition effects in various PDx models for mice treated with RAD1901 alone and/or a RAD1901-palbo combination. Twelve patient-derived xenograft models were screened to test RAD1901 response in a variety of genetic backgrounds with varied levels of ER, PR and Her2. Full efficacy study was carried out for PDx models marked with “*” (PDx-1 to PDx-4, and PDx-12), with n=8-10. These PDx models were treated with vehicle (negative control), RAD1901 at a dosage of 60 mg/kg p.o., q.d., or a RAD1901-palbo combination with 60 mg/kg RAD1901 and palbociclib p.o., q.d. for 60 days. Screen study was carried out for other PDx models (PDx-5 to PDx-11), with n=3 at treated with vehicle (negative control) or RAD1901 at a dosage of 90 mg/kg, for 60 days, p.o., q.d. As demonstrated in FIG. 1, PDx models in which the growth was driven by ER and an additional driver (e.g., PR+ and/or Her2+) benefited from the RAD1901 treatments. RAD1901 was efficacious in inhibiting tumor growth in models with ER mutations and/or high level expression of Her2 (PDx), regardless of prior treatment, either treatment naïve (Rx-naïve), or treated with aromatase inhibitor, tamoxifen (tam), chemotherapy (chemo), Her2 inhibitors (Her2i, e.g., trastuzumab, lapatinib), bevacizumab, fulvestrant, and/or rituximab.

RAD1901-palbo combinations demonstrated enhanced tumor growth inhibition in PDx models in which RAD1901 single agent treatment achieved TGI of 64% or lower (PDx-2, PDx-5, PDx-7, PDx-8, PDx-9, and PDx-10). Said PDx models include treatment naïve models (PDx-2, ER++, PR++ and Her2+), and models with prior treatments of aromatase inhibitor (AI, tamoxifen (tam), chemotherapy (chemo), Her2 inhibitors (Her2i, e.g., trastuzumab, lapatinib), bevacizumab, fulvestrant, and/or rituximab (PDx-5, PDx-7, PDx-8, PDx-9, and PDx-10). PDx-5 models expressed mutant ESR1, while other PDx models expressed WT ESR1. PDx-2, and PDx-5 models were PR+ and Her2+, while other PDx models were PR- and HER2+. Because RAD1901 single agent treatment provided TGI of 65% or higher in PDx-6 and PDx-11 models, the differences between RAD1901 treatment with and without palbociclib could not be demonstrated in FIG. 1. See, e.g., Example (I)(A)(ii), and FIG. 3B showing RAD1901-palbo combinations caused more significant tumor regression than RAD1901 alone in PDx11 models.

I(A)(ii) RAD1901-palbo combination drove more regression than RAD1901 alone in xenograft models expressing W7′ ER

I(A)(ii)(1) RAD1901-palbo drove more regression than RAD1901 alone in MCF-7 xenografts that were responsive to fulvestrant treatments.

MCF7 Xenograft Model

Two days before cell implantation, Balb/C-Nude mice were inoculated with 0.18/90-day release 17β-estradiol pellets. MCF7 cells (PR+, Her2-) were harvested and 1×10⁷ cells were implanted subcutaneously in the right flank of Balb/C-Nude mice. When the tumors reached an average of 200 mm³, the mice were randomized into treatment groups by tumor volume and treated with the test compounds. Each group was treated with vehicle (control, p.o., q.d. to the endpoint), fulvestrant (Faslodex®; 3 mg/subject, s.c., qwk×5 and extended if necessary), RAD1901 (30 mg/kg or 60 mg/kg of the subject, p.o., q.d. to the endpoint), palbociclib (45 mg/kg or 75 mg/kg or 100 mg/kg, p.o., q.d. to the end point), or RAD1901-palbo combination at doses specified from day 0. The treatment period lasted for 28 days.

FIGS. 2A-C demonstrate that in MCF7 Xenograft Model, RAD1901-palbo combination with RAD1901 at 60 mg/kg p.o., q.d. and palbociclib at 45 mg/kg p.o., q.d. RAD1901 (60 mg/kg p.o., q.d.) significantly reduced tumor size by about 50% by day 14. RAD1901 and palbociclib when administered alone exhibited efficacy in inhibiting tumor growth.

To confirm these results, MCF7 xenograft mice were treated with vehicle (negative control), RAD1901 (30 or 60 mg/kg, p.o., q.d), palbociclib (45 mg/kg, p.o., q.d), a combination of RAD1901 (30 or 60 mg/kg, p.o., q.d) and palbociclib (45 mg/kg, p.o., q.d), fulvestrant (3 mg/dose, s.c., qwk) or a combination of fulvestrant (3 mg/dose, s.c., qwk) and palbociclib (45 mg/kg, p.o., q.d.). Tumor size was measured at various time points for 27 days.

Results are shown in FIGS. 2A-B. Treatment with the combination of RAD1901 (60 mg/kg) and palbociclib (45 mg/kg) once again resulted in significant tumor regression, with superior results to treatment with RAD1901, palbociclib, or fulvestrant alone, or with a combination of fulvestrant and palbociclib (FIGS. 2A-B).

FIG. 2C demonstrates that RAD1901-palbo combinations with RAD1901 at a dose of 30 mg/kg or 60 mg/kg both provided similar effects, although RAD1901 alone at 30 mg/kg was not as effective as RAD1901 alone at 60 mg/kg in inhibiting tumor growth. Said results suggest a RAD1901-palbo combination with a lower dose of RAD1901 (e.g., 30 mg/kg) was sufficient to maximize the tumor growth inhibition/tumor regression effects in said xenograft models.

Treatment with the combination of RAD1901 and palbociclib was also more effective at decreasing ER and PR expression in vivo in the MCF7 xenograft models than treatment with RAD1901, palbociclib, or fulvestrant alone, or treatment with a combination of fulvestrant and palbociclib (FIG. 13); tumors harvested two hours after the last dosing).

I(A)(ii)(2) RAD1901-Palbo Drove More Tumor Regression than RAD1901 Alone in PDx-11 and PDx-2 Models that were Responsive to Fulvestrant Treatments.

ER WT PDx models PDx-2 (PR+, Her2+, treatment naïve) and PDx-11 (PR+, Her2+, treated with AI, fulvestrant and chemo) exhibited different sensitivities to fulvestrant (3 mg/dose, s.c., qwk). PDx-2 and PDx-11 models were treated with a combination of RAD1901 (60 mg/kg, p.o., q.d.) and palbociclib (75 mg/kg, p.o., q.d.), RAD1901 alone (60 mg/kg, p.o., q.d.), palbociclib alone (75 mg/kg, p.o., q.d.), or fulvestrant alone (3 mg/dose, s.c., qwk). PDx-11 models were also treated with a combination of palbociclib (75 mg/kg, p.o., q.d.), and fulvestrant (3 mg/dose, s.c., qwk).

In PDx-11 models, administration of fulvestrant or palbociclib alone significantly inhibited tumor growth, with fulvestrant treated mice exhibiting better effects in tumor growth inhibition. The ful-palbo combination exhibited slight tumor regression. Unexpectedly, administration of RAD1901 alone or in combination with palbociclib resulted in a significant tumor regression, with the combination achieved even more significant tumor regression effects in the wild-type ESR1 PDx models (FIG. 3B)).

In PDx-2 models, oral administration of RAD1901 alone achieved better effects of inhibiting tumor growth comparing to injection of fulvestrant alone (FIG. 4A). Furthermore, administration of RAD1901 or palbociclib alone significantly inhibited tumor growth. Unexpectedly, administration of RAD1901 in combination with palbociclib resulted in even more enhanced effect in inhibiting tumor growth (FIG. 4B)).

Furthermore, in PDx-4 model that were responsive to fulvestrant treatment (1 mg/dose, qwk, s.c.), RAD1901-mediated tumor growth inhibition was maintained in the absence of treatment at least two months after RAD1901 treatment (30 mg/kg, p.o., q.d.) period ended, while estradiol treatment continued (FIG. 5).

Thus, a RAD1901-palbo combination is likely to benefit a patient in inhibiting tumor growth after treatment ends, especially when CDK4/6 inhibitors (e.g., ribociclib, abemaciclib and palbociclib) can only be administered intermittently due to their side effects (O'Leary).

I(A)(iii) RAD1901-Palbo Drove More Regression than RAD1901 Alone in Xenograft Models Expressing Mutant ER (ERα Y537S)

I(A)(iii)(1) RAD1901-Palbo Drove More Regression than RAD1901 Alone in PDx-5 Models that were Hardly Responsive to Fulvestrant Treatments.

PDx-5 models were prepared following similar protocol as described supra for PDx models. The tumor sizes of each dosing group were measured twice weekly with Vernier calipers, and volumes were calculated using the formula (L*W2)*0.52.

Inhibition of tumor growth by RAD1901 (60 mg/kg, p.o., q.d.), palbociclib (100 mg/kg, dropped to 75 mg/kg mid-study due to tolerability issues, p.o., q.d.), and RAD1901 (60 mg/kg, p.o., q.d.) in combination with palbociclib (100 mg/kg, dropped to 75 mg/kg mid-study due to tolerability issues) in mutant ER PDx-5 models (PDx models with patient-derived breast cancer tumor having the Y537S estrogen receptor mutation, PR+, Her2+, prior treatment with aromatase inhibitor) was assessed using the method described supra. For tumors expressing certain ERα mutations (e.g., Y537S), combination treatment of RAD1901 and palbociclib was more effective in inhibiting tumor growth than treatment with either agent alone (FIG. 6A)). These PDx models were not sensitive to fulvestrant (3 mg/dose) treatment (FIG. 6A). Combination treatment of RAD1901 and palbociclib was more effective than treatment with either agent alone in driving tumor regressions in the RDx-5 models (FIGS. 6B-C), showing the change of the individual tumor size from baseline on day 17 and day 56, respectively).

PDx-5 was treated with vehicle (negative control), fulvestrant (faslodex 3 mg/dose, s.c., qwk), RAD1901 (60 mg/kg or 120 mg/kg, p.o., q.d.), palbociclib (100 mg/kg, p.o., q.d., dropped to 75 mg/kg mid-study due to tolerability issues), or the combination of RAD1901 (60 or 120 mg/kg, p.o., q.d.) and palbociclib (100 mg/kg, p.o., q.d., dropped to 75 mg/kg mid-study due to tolerability issues). The tumor sizes measured were shown in (FIGS. 7A-B). PDx-5 models were resistant to fulvestrant treatment, but RAD1901 and palbociclib either alone or in combination inhibited tumor growth. At a dose of 60 mg/kg, RAD1901 alone had substantially the same efficacy as palbociclib alone at 100 mg/kg (FIG. 7A); while at a dose of 120 mg/kg, RAD1901 alone had an improved efficacy comparing to palbociclib alone at 100 mg/kg (FIG. 7B). RAD1901 at 60 mg/kg p.o. achieved significant inhibition of tumor growth (FIG. 8). Furthermore, administration of palbociclib alone or in combination with fulvestrant significantly inhibited tumor growth in the mutant PDx model, although the combination did not further enhance the inhibition (FIG. 8).

Unexpectedly, RAD1901 alone or in combination with palbociclib achieved even more significant tumor inhibition, with the combination almost completely inhibited tumor growth in the mutant PDx model; and a RAD1901-palbo combination with a lower dose of RAD1901 (e.g., 60 mg/kg) was sufficient to maximize the tumor growth inhibition/tumor regression effects in PDx-5 models (FIGS. 7A-B).

Thus, the results showed that RAD1901 was an effective endocrine backbone that potentiated the tumor growth inhibition of targeted agents. Furthermore, RAD1901 showed potent anti-tumor activity in PDx models derived from patients that have had multiple prior endocrine therapies including those that are insensitive to fulvestrant.

I(A)(iv) Pharmacokinetic Evaluation of Fulvestrant Treatments to Non-Tumor Bearing Mice.

Various doses of fulvestrant were administered to mice and demonstrated significant dose exposure to the subjects (Figure. 9).

Fulvestrant was administered at 1, 3, or 5 mg/dose subcutaneously to nude mice on day 1 (D1 Rx) and day 8 (D8 Rx, n=4/dose level). Blood was collected at the indicated time points for up to 168 hours after the second dose, centrifuged, and plasma was analyzed by Liquid Chromatography-Mass Spectrometry.

I(B) RAD1901 Promoted Survival in a Mouse Xenograft Model of Brain Metastasis (MCF-7 Intracranial Models).

The potential ability of RAD1901 to cross the blood-brain barrier and inhibit tumor growth was further evaluated using an MCF-7 intracranial tumor xenograft model.

Female athymic nude mice (Crl:NU(NCr)-Foxnlnu) were used for tumor xenograft studies. Three days prior to tumor cell implantation, estrogen pellets (0.36 mg E2, 60-day release, Innovative Research of America, Sarasota, Fla.) were implanted subcutaneously between the scapulae of all test animals using a sterilized trochar. MCF-7 human breast adenocarcinoma cells were cultured to mid-log phase in RPMI-1640 medium containing 10% fetal bovine serum, 100 units/mL penicillin G, 100 μg/mL streptomycin sulfate, 2 mM glutamine, 10 mM HEPES, 0.075% sodium bicarbonate and 25 g/mL gentamicin. On the day of tumor cell implant, the cells were trypsinized, pelleted, and resuspended in phosphate buffered saline at a concentration of 5×10⁷ cells/mL. Each test mouse received 1×10⁶ MCF-7 cells implanted intracranially.

Five days after tumor cell implantation (designated as day 1 of the study), mice were randomized into three groups of 12 animals each and treated with vehicle, fulvestrant (0.5 mg/animal q.d.), or RAD1901 (120 mg/kg q.d.), as described above.

The endpoint was defined as a mortality or 3× survival of the control group, whichever comes first. Treatment tolerability was assessed by body weight measurements and frequent observation for clinical signs of treatment-related adverse effects. Animals with weight loss exceeding 30% for one measurement, or exceeding 25% for three measurements, were humanely euthanized and classified as a treatment-related death. Acceptable toxicity was defined as a group-mean body weight loss of less than 20% during the study and not more than one treatment-related death among ten treated animals, or 10%. At the end of study animals were euthanized by terminal cardiac puncture under isoflurane anesthesia. RAD1901 and fulvestrant concentration in plasma and tumor were determined using LC-MS/MS.

Kaplan Meier survival analysis demonstrated that RAD1901 significantly prolonged survival compared to fulvestrant (P<0.0001; FIG. 10). No animals in the control or fulvestrant group survived beyond day 20 and day 34 respectively, whereas 41% (5/12) of the RAD1901 treated animals survived until the end of the study on day 54.

Concentration of RAD1901 in the plasma was 738±471 ng/mL and in the intracranial tumor was 462±105 ng/g supporting the hypothesis that RAD1901 is able to effectively cross the blood-brain barrier. In contrast, concentrations of fulvestrant were substantially lower in the plasma (21±10 ng/mL) and in the intracranial tumor (8.3±0.8 ng/g).

Example II. RAD1901 Preferably Accumulated in Tumor and could be Delivered to Brain

MCF-7 xenografts as described in Example I(A)(i) were further evaluated for RAD1901 concentration in plasma and tumor using LC-MS/MS. At the end of study, the concentration of RAD1901 in plasma was 344±117 ng/mL and in tumor in 11,118±3,801 ng/mL for the 60 mg/kg dose level. A similar tumor to plasma ratio was also observed at lower dose levels where tumor concentrations were approximately 20-30 fold higher than in plasma. RAD1901 levels in plasma, tumor, and brain for mice treated for 40 days are summarized in Table 1. A significant amount of RAD1901 was delivered to the brain of the treated mice (e.g., see the B/P ratio (RAD1901 concentration in brain/the RAD1901 concentration in plasma)), indicating that RAD1901 was able to cross the blood-brain barrier (BBB). Unexpectedly, RAD1901 preferably accumulated in the tumor. See, e.g., the T/P (RAD1901 concentration in tumor/RAD1901 concentration in plasma) ratio shown in Table 1.

Example III. RAD1901 Inhibited ER Pathway and Degraded ER

III(A). RAD1901 Decreased ER-Engagements in Uterus and Pituitary in Healthy Postmenopausal Female Human Subjects.

The subjects had an amenorrhea duration of at least 12 months and serum FSH consistent with menopause. The subjects were 40-75 years old with BMI of 18.0-30 kg/m². Subjects had intact uterus. Subjects having evidence of clinically relevant pathology, increased risk of stroke or of history venous thromboembolic events, or use of concomitant medication less than 14 days prior to admission to clinical research center (paracetamol allowed up to 3 days prior) were excluded.

FES-PET was performed at baseline and after 6 days of exposure to RAD1901 to evaluate ER engagement in the uterus. RAD1901 occupied 83% and 92% of ER in the uterus at the 200 mg (7 subjects) and 500 mg (6 subjects) dose levels, respectively.

FES-PET imaging showed significant reduction in binding of labeled-estradiol to both the uterus and pituitary after RAD1901 treatment with 200 mg or 500 mg (p.o., q.d, 6 days).

Due to the high ER expression, the uterus showed a strong FES-PET signal at baseline before RAD1901 treatment (FIG. 11A), baseline transversal view for uterus FES-PET scan of Subject 3 treated with 200 mg dose level; FIG. 11B, baseline sagittal view and transversal view for uterus FES-PET scan respectively of Subject 7 treated with 500 mg dose level). However, when scanned four hours post dosing on day 6 in the study, the uterus was hardly visible (at or close to background FES-PET signal (FIG. 11A), Day 6 transversal view for uterus scan of Subject 3; and FIG. 11B, Day 6 sagittal view and transversal view for uterus scan respectively of Subject 7). Such data were consistent with ER degradation and/or competition for the binding to the receptor. FIGS. 11A-B also include CT scan of the uterus scanned by FES-PET showing the existence of the uterus before and after RAD1901 treatment.

The FES-PET uterus scan results were further quantified to show the change of post-dose ER-binding from baseline for 7 subjects (FIG. 11(C)), showing Subjects 1-3 and Subjects 4-7 as examples of the 200 mg dose group and 500 mg dose group, respectively. RAD1901 showed robust ER engagement at the lower dose level (200 mg).

FIG. 12 showed a representative image of FES-PET scan of the uterus (A) and pituitary (B) before (Baseline) and after (Post-treatment) RAD1901 treatment at 500 mg p.o., q.d., for six days. FIG. 12A showed the FES-PET scan of the uterus by (a) Lateral cross-section; (b) longitude cross-section; and (c) longitude cross-section.

The subject's post dose FES-PET scan of uterus and pituitary showed no noticeable signal of ER binding at uterus (FIG. 12A, Post-treatment) and at pituitary (FIG. 12B, Post-treatment), respectively.

Thus, the results showed that RAD1901 effectively engaged ER in human at a dosage of 200 and 500 mg p.o., q.d., for six days.

Standard uptake value (SUV) for uterus, muscle and bone were calculated and summarized for RAD1901 treatments at 200 mg and 500 mg p.o., q.d. in Tables 2 and 3, respectively. Post-dose uterine signals were at or close to levels from “non-target tissues,” suggesting a complete attenuation of FES-PET uptake post RAD1901 treatment. Almost no change was observed in pre-versus post-treatment PET scans in tissues that did not significant express estrogen receptor.

Thus, RAD1901 or salt or solvate (e.g., hydrate) thereof may be used in treating cancer and/or tumor cells having overexpression of ER (e.g., breast cancer, uterus cancer, and ovary cancer), without negative effects to other organs (e.g. bones, muscles). RAD1901 or salt or solvate (e.g., hydrate) thereof may be especially useful in treating metastatic cancers and/or tumors having overexpression of ER in other organs, e.g., the original breast cancer, uterus cancer, and/or ovary cancer migrated to other organs (e.g., bones, muscles), to treat breast cancer, uterus cancer, and/or ovary cancer lesions in other organs (e.g., bones, muscles), without negative effect to said organs.

III(B). RAD1901 Decreased ER Expression and Inhibited ER Pathway.

III(B)(i)(1) RAD1901-Palbo Combo was More Effective in Decreasing ER and PR Expression in MCF7 Xenograft Models and Treatment with RAD1901, Palbociclib or Fulvestrant Alone, or a Ful-Palbo Combination.

Treatment with the combination of RAD1901 and palbociclib was also more effective at decreasing ER and PR expression in vivo in the MCF7 xenograft models (as described in Example I(A)(ii)) than treatment with RAD1901, palbociclib, or fulvestrant alone, or treatment with a combination of fulvestrant and palbociclib (FIG. 13); tumors harvested two hours after the last dosing).

III(B)(i)(2) Comparison of RAD1901 and Fulvestrant in MCF7 and T47D Cell Lines.

The effects of RAD1901 and fulvestrant were compared using MCF7 and T47D cell lines, both are human breast cancer cell lines, at various concentrations, 0.01 μM, 0.1_(R)M and 1 μM (FIG. 14A for MCF7 cell line assays; and FIG. 14B for T47D cell lines). Three ER target genes, progesterone receptor (PgR), growth regulation by estrogen in breast cancer 1 (GREB1) and trefoil factor 1 (TFF1), were used as markers. RAD1901 caused ER degradation and inhibited ER signaling (FIG. 14). Unexpectedly, RAD1901 was comparable or more effective than fulvestrant in inhibiting tumor growth, and driving tumor regression as disclosed supra in Example I(A) and Example I(B).

III(B)(i)(3) RAD1901 Treatment Resulted in ER Degradation and Abrogation of ER Signaling in MCF7 Xenograft Model—Described Supra in Example I(A)(ii)(1).

RAD1901 treatment resulted in ER degradation in vivo (FIGS. 15A-C, student's t-test: *p-value<0.05, **p-value<0.01) and inhibited of ER signaling in vivo (FIGS. 15A and 15C, student's t-test: *p-value<0.05, **p-value<0.01).

Tumor harvested from MCF7 xenograft 2 hours after the final dose of RAD1901 (30 mg/kg, 60 mg/kg, p.o., q.d.) or fulvestrant (3 mg/dose, s.c., qwk) showed significantly decreased ER and PR expression (FIGS. 15A-B). Tumor harvested from MCF7 xenograft 8 hours after the final dose of fulvestrant treatment showed varied PR and ER expression. However, tumor harvested from MCF7 xenograft 8 hours after the final dose of RAD1901 treatment showed reduced PR and ER expression (FIGS. 15A and 15C).

Tumor harvested from MCF7 xenograft 8 hours or 12 hours after the single dose of RAD1901 (30 mg/kg, 60 mg/kg, or 90 mg/kg, p.o., q.d.) showed rapidly decreased PR expression (FIG. 16A). Tumor harvested from MCF7 xenograft 4 hours or 24 hours after the 7th dose of RAD1901 (30 mg/kg, 60 mg/kg, or 90 mg/kg, p.o., q.d.) showed consistent and stable inhibition of ER signaling (FIG. 16B). Quantification of western blot analyses of tumor harvested from MCF7 xenograft at various time points during the treatment of RAD1901 (30 mg/kg, 60 mg/kg, or 90 mg/kg, p.o., q.d.) showed a dose-dependent decrease in PR (FIG. 16c ).

RAD1901 treatment caused a rapid decrease in proliferation in MCF7 xenograft models. For example, tumor harvested from MCF7 xenograft models 8 hours after the single dose of RAD1901 (90 mg/kg, p.o., q.d.) and 24 hours after the 4th dose of RAD1901 (90 mg/kg, p.o., q.d.) were sectioned and stained to show a rapid decrease of the proliferation marker Ki67 (FIGS. 17A-B).

These results suggest that RAD1901 treatment results in ER degradation and inhibition of ER signaling in ER WT xenografts in vivo.

III(B)(i)(4) RAD1901 Treatment Resulted in ER Degradation and Abrogation of ER Signaling in PDx-4 Models Described Supra in Example I(A)(ii).

RAD1901 treatment caused a rapid decrease in proliferation in the PDx-4 models. For example, four hours after the final dose on the last day of a 56 day efficacy study, tumor harvested from PDx-4 models treated with RAD1901 (30, 60, or 120 mg/kg, p.o., q.d.) or fulvestrant (1 mg/animal, qwk) were sectioned and showed a rapid decrease of the proliferation marker Ki67 compared to PDx-4 models treated with fulvestrant (FIG. 18).

These results suggest that RAD1901 treatment results in ER degradation and inhibition of ER signaling in ER WT xenografts in vivo.

III(B)(ii) RAD1901 Treatment Resulted in Decreased ER Signaling in a Mutant ER Xenograft PDx-5 Models Described Supra in Example I(A)(iii)(1).

Tumors were harvested at the indicated time points after the last day of dosing (unless otherwise specified), homogenized in RIPA buffer with protease and phosphatase inhibitors using a Tissuelyser (Qiagen). Equal amounts of protein were separated by MW, transferred to nitrocellulose membranes and blotted with the following antibody as described in the Materials and methods section: progesterone receptor (PR, Cell Signaling Technologies; 3153).

Bands were quantified using 1D Quant software (GE), and PR IHC Allred scores obtained from PDx-5 models as described in Example I(A)(iii)(1) are shown in FIG. 19. Fulvestrant exerted little influence to PR expression, while RAD1901 showed efficacy at dosages of both 60 mg/kg and 120 mg/kg (p.o., q.d., III(B)(ii)-FIG. 1).

These results indicate that for tumors expressing certain ERα mutations (e.g., Y537S), RAD1901 was more effective than fulvestrant at inhibiting the tumor growth, especially effective in inhibiting the growth of tumors which were hardly responsive to fulvestrant treatment (e.g., at a dosage of 3 mg/dose, s.c., qwk, FIG. 6A for PDx-5). Furthermore, for the tumors which did not respond well to fulvestrant treatment (e.g., PDx-5), RAD1901 was effective in reducing PR expression in vivo, while fulvestrant was not (FIG. 19).

Example IV Impact of RAD1901 Treatment to Uterine Tissue and/or BMD

IV(a(1)): RAD1901 Antagonized Estradiol Stimulation of Uterine Tissue.

The uterotropic effects of RAD1901 were investigated by assessing changes in uterine weight, histology, and C3 gene expression in immature rats. Results from a representative study are shown in FIGS. 20A-D.

Assessment of Uterotropic Activity

Sprague-Dawley rat pups were weaned at 19 days of age, randomized into groups (n=4), and administered vehicle (aqueous methylcellulose), E2 (0.01 mg/kg), raloxifene (3 mg/kg), tamoxifen (1 mg/kg), RAD1901 alone (0.3 to 100 mg/kg), or RAD1901 (0.01 to 10 mg/kg) in combination with E2 (0.01 mg/kg), either s.c. or p.o. as appropriate (see reagents, above), q.d., for 3 consecutive days. Twenty-four hours after the final dose, all animals were euthanized by carbon dioxide inhalation. Body weights and wet uterine weights were recorded for each animal. Similar assays were also conducted with RAD1901 (0.03 to 100 mg/kg) in rats and mice (Charles River Laboratories, Montreal, QC).

Fresh uterine tissue from each rat was fixed in 4% paraformaldehyde, dehydrated with ethanol, and embedded into JB4 plastic resin. Sections were cut at 8 μm and stained with 0.1% Toluidine Blue O. Thickness of the endometrial epithelium was measured using a Zeiss Axioskop 40 microscope using the Spot Advanced program; the mean of 9 measurements per specimen was calculated.

Uterine Complement Component 3 (C3) Gene Expression

To determine relative expression levels of C3 in the treated uterine tissue, RNA was extracted from the remaining tissue using the Micro to Midi Total RNA Purification Kit (Invitrogen, Carlsbad, Calif.) according to the manufacturer's instructions. RNA was quantified, and equal amounts were reverse-transcribed using the High Capacity cDNA Archive Kit (Applied Biosystems, Foster City, Calif.).

Quantitative PCR was performed using the ABI Prism 7300 System (Applied Biosystems). PCR was done using the Taqman Universal Master Mix with probe sets for C3 and for the 18S ribosomal RNA as a reference gene. Thermal cycling conditions comprised an initial denaturation step at 95° C. for 10 min, followed by 40 cycles at 95° C. for 15 second and 60° C. for 1 minute.

Relative gene expression was determined by normalizing each sample to the endogenous control (18S) and comparing with a calibrator (vehicle). Relative gene expression was determined using the following equation: 2-ΔΔCt (where Ct=cycle threshold or the cycle number at which PCR product was first detected, ΔCt=normalized sample value, and ΔΔCt=normalized difference between dosed subjects and the vehicle). Five replicate gene expression determinations were conducted for each dose, within each study.

Treatment with E2 (0.01 mg/kg), raloxifene (RAL, 3 mg/kg) or tamoxifen (TAM, 1 mg/kg) resulted in significant increases in uterine wet weight compared to vehicle alone, whereas RAD1901 treatment at a range of doses between 0.3 and 100 mg/kg did not significantly affect uterine wet weight (FIG. 20A). Data shown (FIG. 20A) are means (±SEM); n=4 rats per group; P vs. vehicle: *<0.05; vs. E2: ‡<0.05. Further, when administered in combination with E2 (0.01 mg/kg), RAD1901 antagonized E2-mediated uterine stimulation in a dose-dependent manner, exhibiting significant inhibition of uterotropic activity at doses of 0.1 mg/kg and greater and complete inhibition at 3 mg/kg. The EC₅₀ for RAD1901 was approximately 0.3 mg/kg. Similar results were obtained in mice where RAD1901 doses 0.03 to 100 mg/kg also had no effect on uterine wet weight or epithelial thickness (data not shown).

Treatment-dependent changes in uterine tissue were further investigated by quantitative microscopic histology. There was a statistically significant increase in endometrial epithelial thickness after treatment with E2 at both 0.01 and 0.3 mg/kg (FIG. 20B). A significant increase in epithelial thickness was also observed after treatment with tamoxifen (1 mg/kg) or raloxifene (3 mg/kg). In contrast, RAD1901 treatment did not increase endometrial epithelial thickness up to the highest evaluated dose of 100 mg/kg. Representative images of the endometrial epithelium are shown in FIG. 20C.

Consistent with the changes in both uterine weight and endometrial epithelial thickness, E2, tamoxifen, and raloxifene all significantly increased the expression of the estrogen-regulated complement gene, C3 (FIG. 20D)). In contrast, RAD1901 did not increase C3 gene expression at any of the doses tested (0.3 to 100 mg/kg). Furthermore, RAD1901 at 1, 3 and 10 mg/kg significantly suppressed E2-stimulated C3 gene expression.

RAD1901 Did not Stimulate the Uterus of Immature Female Rats

Immature female rats were administered p.o., q.d., for 3 consecutive days with vehicle (VEH), estradiol (E2), Raloxifene (RAL), Tamoxifen (TAM), RAD1901 or RAD1901+E2. Wet uterine weights were measured. Data shown (FIG. 20A) are means (±SEM); n=4 rats per group; P vs. vehicle: *<0.05; vs. E2: ‡<0.05.

Example II(A)(2). Treatment with RAD1901 Protected Against Bone Loss in Ovariectomized Rats

The bone-specific effects of RAD1901 was examined in ovariectomized rats.

As a model of postmenopausal bone loss, ovariectomy was performed on anesthetized adult female Sprague-Dawley rats, with sham surgery as a control. Following surgery, ovariectomized rats were treated q.d. for 4 weeks with vehicle, E2 (0.01 mg/kg), or RAD1901 (0.1, 0.3, 1, 3 mg/kg), administered as described above, with 20 animals per group. Animals in the sham surgery group were vehicle treated. All animals were euthanized by carbon dioxide inhalation 24 hours after the final dose. Bone mineral density was assessed at baseline and again after 4 weeks of treatment using PlXImus dual emission x-ray absorptiometry.

At necropsy, the left femur of each animal was removed, dissected free of soft tissue and stored in 70% ethanol before analysis. A detailed qualitative and quantitative 3-D evaluation was performed using a micro-CT40 system (Scanco Systems, Wayne, Pa.). For each specimen, 250 image slices of the distal femur metaphysis were acquired. Morphometric parameters were determined using a direct 3-D approach in pre-selected analysis regions. Parameters determined in the trabecular bone included bone volume density, bone surface density, trabecular number, trabecular thickness, trabecular spacing, connectivity density, and apparent bone density.

Following ovariectomy, untreated (vehicle control) rats experienced a decrease in bone mineral density both in the whole full femur and in the lumbar spine compared to baseline (Table 5). Treatment with E2 was associated with prevention of bone loss in both the femur and spine. Treatment with RAD1901 resulted in a dose-dependent and statistically significant suppression of ovariectomy-induced bone loss (data shown for the 3 mg/kg treatment group). At doses of 0.1 mg/kg to 3 mg/kg, bone mineral density in RAD1901-treated rats was complete, with no statistically significant difference from the E2-treated group.

Micro-CT analysis of the distal femur (Table 6) demonstrated that ovariectomy induced significant changes in a number of key micro-architectural parameters when compared to sham surgery animals. These changes were consistent with a decrease in bone mass and include decreased bone volume, reduced trabecular number, thickness and density, and increased trabecular separation. Consistent with the preservation of bone mineral density observed after treatment with RAD1901, significant preservation of trabecular architecture was observed in key micro-structural parameters (Table 6)

Example IV(B): Phase 1 Dose Escalation Study of RAD101 in Healthy Postmenopausal Women

In the phase 1 study, safety, tolerability and pharmacokinetics were evaluated in 44 healthy postmenopausal females. No dose limiting toxicites (DLT) were observed, maximum tolerated dose (MTD) was not established. Plasma exposure increased more than dose proportionally over the dose range tested.

Subjects

44 healthy postmenopausal females were enrolled as subjects for this phase 1 study. The subjects had an amenorrhea duration of at least 12 months and serum FSH consistent with menopause. The subjects were 40-75 years old with BMI of 18.0-30 kg/m². Subjects having evidence of clinically relevant pathology, increased risk of stroke or of history venous thromboembolic events, or use of concomitant medication less than 14 days prior to admission to clinical research center (paracetamol allowed up to 3 days prior) were excluded.

Dosing

The subjects were treated with placebo or at least one dose p.o., q.d. after a light breakfast for 7 days at dose levels of 200 mg, 500 mg, 750 mg and 1000 mg, respectively. The key baseline demographics of the 44 healthy postmenopausal females enrolled in the phase 1 study are summarized in Table 7.

Treatment Emergent Adverse Events (TEAEs)

TEAEs were recorded, and the most frequent (>10% of patients in the total active group who had any related TEAEs) adverse events (AEs) are summarized in Table 8, “n” is number of subjects with at least one treatment-related AE in a given category, AEs graded as per the Common Terminology Criteria for Adverse Events (CTCAE) v4.0, and any patient with multiple scenarios of a same preferred term was counted only once to the most severe grade. No dose limiting toxicities were observed, maximum tolerated dose (MTD) was not established.

Pharmacokinetic Evaluations

A series of blood samples were taken during the study for the analysis of RAD1901 in plasma. Blood samples of 5 mL each were taken via an indwelling IV catheter or by direct venipuncture into tubes containing K₃-EDTA as anticoagulant. Steady state was achieved by day 5 of treatment. Geometric Mean (Geo-Mean) plasma concentration-time profiles of RAD1901 were evaluated. Plasma pharmacokinetic results of the groups treated with RAD1901 (200, 500, 750 or 1,000 mg) on Day 7 (N=35) in the study are provided in Table 8 and FIG. 21, as an example. The median t_(1/2) was between 37.5-42.3 hours (Table 8). After multiple dose administration of RAD1901, median t_(max) ranged between 3-4 hours post-dose.

Example V(A)-1. Modeling of RAD1901-ERα Binding Using Select Published ER Structures

Unless specified otherwise, when structures are shown by their stick model, each end of a bond is colored with the same color as the atom to which it is attached, wherein grey is carbon, red is oxygen, blue is nitrogen and white is hydrogen.

Fourteen published structures (i.e., models) of ERα ligand-binding domain (LBD) complexed with various ER ligands were selected from 96 published models by careful evaluation. One of these fourteen models was 3ERT (human ERα LBD bound to 4-hydroxytamoxifen (OHT)). OHT is the active metabolite of tamoxifen and a first generation SERM that functions as an antagonist in breast tissue.

In 3ERT (FIGS. 21 and 22), the ERα binding site adopts a three layer “helical sandwich” forming a hydrophobic pocket which includes Helix 3 (H3), Helix 5 (H5), and Helix 11 (H11) (FIG. 21). The dotted box in FIG. 22 represents the binding site and residues within the binding site that are important or are effected by OHT binding. OHT functions as an antagonist by displacing H12 into the site where LXXLL coactivator(s) binds. OHT occupies the space normally filled by L540 and modifies the conformation of four residues on the C-terminal of Helix 11 (G521, H524, L525, and M528). OHT also forms a salt bridge with D351, resulting in charge neutralization.

The other thirteen ERα LBD-ER ligand models were compared to 3ERT. Differences in their residue poses are summarized in Table 10. Superimposition of the ERα structures of the fourteen models (FIG. 23) shows that these structures differed significantly at residues E380, M421, G521, M522, H524, Y526, 5527, M528, P535, Y537, L540, and various combinations thereof.

Root-mean-square deviation (RMSD) calculations of any pair of the fourteen models are summarized in Table 11. Structures were considered to be overlapping when their RMSD was <2 Å. Table 11 shows that all fourteen models had a RMSD<1.5 Å. Using conditional formatting analysis suggested that 1R5K and 3UUC were the least similar to the other models (analysis not shown). Therefore, 1R5K and 3UUC were considered a unique, separate structural cluster to be examined.

ERα residues bound by ligand in the fourteen models are summarized in Table 12. Table 12 also shows the EC₅₀ in the ERα LBD-antagonist complexes. Out of the fourteen models, thirteen showed H-bond interactions between the ligand and E353; twelve showed pi interactions between the ligand and F404; five showed H-bond interactions between the ligand and D351; six showed H-bond interactions between the ligand and H524; four showed H-bond interactions between the ligand and R394; and one (3UUC) showed interactions between the ligand and T347.

Each of the fourteen models was used to dock a random library of 1,000 compounds plus the ligand the model was published with (the known antagonist) to determine whether the model could identify and prioritize the known antagonist. If the model could identify the known antagonist, the model was determined to be able to predict the pose of its own published ligand. EF₅₀ was then calculated to quantify the model's strength to see how much better it was than a random selection. RAD1901 was docked in the selected models (e.g., FIGS. 24-28). Docking scores of the published ligand and RAD1901 in the models were determined. EC₅₀ was also determined. Visual inspection of RAD1901 showed that it “obeyed” the interactions shown with the published ligands in 1R5K, 1SJ0, 2JFA, 2BJ4, and 2OUZ. No spatial clashes were noticed. In certain embodiments, e.g., in 1R5k and 2BJ4, RAD1901 had a higher docking score than the published ligand.

The evaluation results of nine models (1ERR, 3ERT, 3UCC, 210K, 1R5K, 1SJ0, 2JFA, 2BJ4, and 2OUZ) are summarized in Table 13.

1ERR and 3ERT could not predict the correct pose of their crystallized ligand. RAD1901 did not dock in 3UCC. The tetrahydronaphtaalen in 210K-RAD1901 bound in a non-traditional manner.

The major differences between the models 1R5K, 1SJ0, 2JFA, 2BJ4, and 2OUZ were the residues in the C-term of Helix 11 (G521-M528).

FIG. 24 shows the modeling of RAD1901-1R5K (a) and GW5-1R5K (b). RAD1901 bound with H-bond interactions to E353, R394, and L536; and with p-interaction with F404.

FIG. 25 shows the modeling of RAD1901-1SJ0 (a) and E4D-1SJ0 (b). RAD1901 bound with H-bond interactions to E353, and D351; and with p-interaction with F404.

FIG. 26 shows the modeling of RAD1901-2JFA (a) and RAL-2JFA (b). RAD1901 bound with p-interaction with F404.

FIG. 27 shows the modeling of RAD1901-2BJ4 (a) and OHT-2BJ4 (b). RAD1901 bound with H-bond interactions with E353 and R394; and p-interaction with F404.

FIG. 28 shows the modeling of RAD1901-2IOK (a) and IOK-2IOK (b). RAD1901 bound with H-bond interactions with E353, R394, and D351; and p-interaction with F404.

The published ligands in the models have the following structures:

Example V(A)-2. Induced Fit Docking (IFD) of ERα with RAD1901 and Fulvestrant

Binding conformation of RAD1901 in ERα was further optimized by IFD analysis of the five ERα crystal structures 1R5K, 1SJ0, 2JFA, 2BJ4, and 2OUZ. IFD analysis accounted for the receptor flexibility (upon ligand binding) to accommodate its correct binding conformation.

A library of different conformations for each ligand (e.g., RAD1901 and fulvestrant) was generated by looking for a local minima as a function of rotations about rotatable bonds. The library for RAD1901 had 25 different conformations.

The five ERα crystal structures were prepared and minimized. The corresponding ligand in the published X-ray structures were used to define the ERα binding pocket.

RAD1901 conformations were docked into the prepared ERα structures wherein they were allowed to induce side-chain or back-bone movements to residues located in the binding pocket. Those movements allowed ERα to alter its binding site so that it was more closely conformed to the shape and binding mode of the RAD1901 conformation. In some examples, small backbone relaxations in the receptor structure and significant side-chain conformation changes were allowed in the IFD analysis.

An empirical scoring function was used to approximate the ligand binding free energy to provide a docking score or Gscore. Gscore is also known as GlideScore, which may be used interchangeably with docking score in this example. The docking score was an estimate of the binding affinity. Therefore, the lower the value of the docking score, the “better” a ligand bound to its receptor. A docking score of −13 to −14 corresponded to a very good binding interaction.

The RAD1901 conformations resulted from the IFD analysis with 1R5K, 1SJ0, 2JFA, 2BJ4, and 2OUZ respectively were superimposed to show their differences (FIG. 29-31, shown in stick model). All bonds in each RAD1901 conformation were shown in the same color in FIGS. 29, 30 and 31(a).

The RAD1901 conformations resulted from the IFD analysis with 1R5K (blue) and 2OUZ (yellow) had N-benzyl-N-ethylaniline group of RAD1901 on the front (FIG. 29). The RAD1901 conformations resulted from the IFD analysis with 2BJ4 (green) and 2JFA (pink) had N-benzyl-N-ethylaniline group of RAD1901 on the back (FIG. 30). The RAD1901 conformations resulted from the IFD analysis with 2BJ4 (green), 2JFA (pink) and 1SJ0 (brown) were quite similar as shown by their superimpositions (FIGS. 31(a) and (b)). The RAD1901 IFD docking scores are summarized in V(A)-Table 5.

The IFD of RAD1901 with 2BJ4 showed hydrogen bond interactions with E353 and D351 and pi-interactions with F404 (FIG. 32(a)-(c)). FIG. 32(a) showed regions within the binding site suitable for H-bond acceptor group (red), H-bond donor group (blue) and hydrophobic group (yellow). In FIG. 32(a)-(b), light blue was for carbon for RAD1901. FIG. 33(a)-(c) show a protein-surface interactions of the IFD of RAD1901 with 2BJ4. V(A)-FIGS. 33(a) and (b) are the front view, and FIG. 33(c) is the side view. The molecular surface of RAD1901 was blue in FIG. 33(a), and green in FIG. 33(c). FIG. 33(b)-(c) are electrostatic representation of the solvent accessible surface of ERα, wherein red represented electronegative and blue represented electropositive.

Similar IFD analysis was carried out for fulvestrant with 2BJ4 as described supra. The fulvestrant-2BJ4 IFD resulted in a Gscore of −14.945 and showed hydrogen bond interactions with E353, Y526, and H524 and pi-interactions with F404 (FIG. 34(a)-(c)). FIG. 34(a) showed regions within the binding site suitable for H-bond acceptor group (red), H-bond donor group (blue) and hydrophobic group (yellow). In FIG. 34(a), light blue was for carbon for RAD1901.

FIG. 35(a)-(b) showed RAD1901 and fulvestrant docked in 2BJ4 by IFD both had pi-interactions with F404 and hydrogen bond interactions with E353. Furthermore, RAD1901 had hydrogen bond interaction with D351 (blue representing RAD1901 molecular surface, FIG. 35(b)), while fulvestrant had hydrogen bond interactions with Y526, and H524 (green representing fulvestrant molecular surface, FIG. 35(c)). Superimpositions of 2BJ4 docked with RAD1901 and fulvestrant are shown in FIG. 36(a)-(b). In FIG. 36(a), green represents fulvestrant molecular surface and blue represents RAD1901 molecular surface. In FIG. 36(b), the brown structure is fulvestrant and the blue structure is RAD1901.

Example V(A)-3. Modeling Evaluation of Select ERα Mutations

Effects of various ERα mutations on the C-terminal ligand-binding domain were evaluated. Specific ERα mutations evaluated were Y537X mutant wherein X was S, N, or C; D538G; and S463P.

Y537 resides in Helix 12. It may regulate ligand binding, homodimerization, and DNA binding once it is phosphorylated, and may allow ERα to escape phosphorylation-mediated controls and provide a cell with a potential selective tumorigenic advantage. In addition, it may cause conformational changes that makes the receptor constitutively active.

The Y537S mutation favors the transcriptionally active closed pocket conformation, whether occupied by ligand or not. The closed but unoccupied pocket may account for ERα's constitutive activity (Carlson et al. Biochemistry 36:14897-14905 (1997)). Ser537 establishes a hydrogen-bonding interaction with Asp351 resulting in an altered conformation of the helix 11-12 loop and burial of Leu536 in a solvent-inaccessible position. This may contribute to constitutive activity of the Y537S mutant protein. The Y537S surface mutation has no impact on the structure of the LBD pocket.

Y537N is common in ERα-negative metastatic breast cancer. A mutation at this site may allow ERα to escape phosphorylation-mediated controls and provide a cell with a potential selective tumorigenic advantage. Specifically, Y537N substitution induces conformational changes in the ERα that might mimic hormone binding, not affecting the ability of the receptor to dimerize, but conferring a constitutive transactivation function to the receptor (Zhang et al. Cancer Res 57:1244-1249 (1997)).

Y537C has a similar effect to Y537N.

D538G may shift the entire energy landscape by stabilizing both the active and inactive conformations, although more preferably the active. This may lead to constitutive activity of this mutant in the absence of hormones as observed in hormone-resistant breast cancer (Huang et al., “A newfound cancer-activating mutation reshapes the energy landscape of estrogen-binding domain,” J. Chem. Theory Comput. 10:2897-2900 (2014)).

None of these mutations are expected to impact the ligand binding domain nor specifically hinder RAD1901 binding. Y537 and D538 may cause conformational changes that leads to constitutive receptor activation independent of ligand binding.

Example V(B). In Vitro Binding Assay of ERα Constructs of Wildtype and LBD Mutant with RAD1901 and Other Compounds

In vitro binding assay of ERα constructs of wildtype (WT) and LBD mutant with RAD1901 showed that RAD1901 bound to mutant ERα with a similar affinity as to WT ERα.

ERα constructs of WT and LBD mutant were prepared by expressing and purifying the corresponding LBD residues 302-552 with N-terminal thioredoxin and 6×His tags which were cleaved by TEV protease.

Fluorescence polarization (FP) was used to determine binding of test compounds (RAD1901, fulvestrant, bazedoxifene, raloxifene, tamoxifene, and AZD9496) to ERα as per manufacturer's instructions (Polar Screen, Invitrogen) with 2 nM fluoromone, 100 nM ERα construct of WT or LBD mutant. Each set was carried out in duplicate and tested one test compound to determine the IC₅₀ for different ERα constructs (FIG. 38 for RAD1901 binding essay).

As stated above, the foregoing is merely intended to illustrate various embodiments of the present invention. The specific modifications discussed above are not to be construed as limitations on the scope of the invention. It will be apparent to one skilled in the art that various equivalents, changes, and modifications may be made without departing from the scope of the invention, and it is understood that such equivalent embodiments are to be included herein. All references cited herein are incorporated by reference as if fully set forth herein.

TABLE 1 RAD1901 levels in plasma, tumor and brain of mice implanted with MCF7 cells after treated for 40 days. Dose Plasma Tumor Brain B/P T/P (mg/kg) (ng/mL) (ng/mL) (ng/mL) Ratio Ratio Vehicle BLQ* BLQ BLQ — — RAD1901 0.3 2 11 BLQ — RAD1901 1 3 45 BLQ — RAD1901 3 9 169 7 0.78 18.78 RAD1901 10 39 757 14 0.36 19.41 RAD1901 30 137 3875 72 0.53 28.28 RAD1901 60 334 11117 201 0.60 33.28 *BLQ: below the limit of quantitation

TABLE 2 SUV for uterus, muscle, and bone for a human subject treated with 200 mg dose p.o., q.d., for six days Uterus SUV Bone SUV Muscle SUV Dose % Change % Change % Change 200 mg −85% 16% 0%

TABLE 3 SUV for uterus, muscle, and bone for human subjects (n = 4) treated with 500 mg dose p.o., q.d., for six days. Uterus Mean SUV Mean Uterus Change Muscle Muscle SUV Mean Bone Bone SUV Subject # Scan SUV (%) SUV Change (%) SUV Change (%) 1 Baseline 3.88 0.33 0.36 Day 6 0.58 −85 0.31 −6 0.48 33 2 Baseline 6.47 0.25 0.49 Day 6 0.33 −86 0.42 68 0.55 12 3 Baseline 3.66 0.50 0.41 Day 6 0.58 −84 0.31 −38 0.47 −23 4 Baseline 3.35 0.30 0.40 Day 6 0.41 −88 0.24 −20 0.52 30 Mean −86 1 13

TABLE 4 Effect of RAD1901 on BMD in ovariectomized rats.^(a) Femur BMD Lumbar Spine BMD Treatment (% change) (% change) Sham  3.1 ± 2.4*  2.7 ± 5.0* OVX + veh −5.4 ± 5.1  −10.2 ± 12.8 OVX + E2 −0.5 ± 2.6*  −2.1 ± 12.2* OVX + RAD1901  0.4 ± 2.8*  −1.1 ± 79* ^(a)Adult female rats underwent either sham or ovariectomy surgery before treatment initiation with vehicle, E2 (0.01 mg/kg) or RAD1901 (3 mg/kg) q.d. (n = 20 per treatment group). BMD was measured by dual emission x-ray absorptiometry at baseline and after 4 weeks of treatment. Data are expressed as mean ± SD. *P < 0.05 versus the corresponding OVX + Veh control. BMD, bone mineral density; E2, beta estradiol; OVX, ovariectomized; Veh, vehicle.

TABLE 5 Effect of RAD1901 on femur microarchitecture in ovariectomized rats^(a) BV/TV ConnD TbN TbTh TbSp ABD Treatment (%) (1/mm³) (1/mm) (mm) (mm) (mgHA/ccm) Sham 0.394 ± 0.069* 138 ± 21* 5.2 ± 0.6* 0.095 ± 0.008* 0.175 ± 0.029* 456 ± 61* OVX + Veh 0.234 ± 0.065  91 ± 32 3.5 ± 0.9 0.085 ± 0.011 0.307 ± 0.086 301 ± 69 OVX + E2 0.309 ± 0.079* 125 ± 25* 4.8 ± 0.8* 0.086 ± 0.008 0.204 ± 0.054* 379 ± 75* OVX + RAD1901 0.300 ± 0.066* 113 ± 22* 4.5 ± 0.8* 0.088 ± 0.008 0.218 ± 0.057* 370 ± 66* ^(a)Adult female rats underwent either sham or ovariectomy surgery before treatment initiation with vehicle, E2 (0.01 mg/kg) or RAD1901 (3 mg/kg) q.d. (n = 20 per treatment group). After 4 weeks, Bone microarchitecture was evaluated using microcomputed tomography. Data are expressed as mean ± SD. *P < 0.05 versus the corresponding OVX + Veh control. ABD, apparent bone density; BV/TV, bone volume density; ConnD, connectivity density; E2, beta estradiol; OVX, ovariectomized; TbN, trabecular number; TbTh, trabecular thickness; TbSp, trabecular spacing; Veh, vehicle.

TABLE 6 Key baseline demographics of Phase 1 dose escalation study of RAD1901 RAD1901 RAD1901 RAD1901 RAD1901 Placebo 200 mg 500 mg 750 mg 1,000 mg (N = 8) (N = 15) (N = 14) (N = 8) (N = 7) Race white 8(100) 14(93) 10(71) 8(100) 7(100) (% of the cohort) Mean age, 64 62 59 64 64 years Mean BMI, 26.1 25 24.4 24.9 26.7 kg/m²

TABLE 7 Most frequent (>10%) treatment related AEs in a Phase 1 dose escalation study of RAD1901 Placebo 200 mg 500 mg 750 mg N = 8 N = 15 N = 14 N = 8 n (%) n (%) n (%) n (%) Gr1 Gr2 Gr3 Gr1 Gr2 Gr3 Gr1 Gr2 Gr3 Gr1 Gr2 Gr3 Nausea 2 (25) 0 0 5 (33) 0 0 3 (21) 2 (14) 0 2 (25) 1 (13) 0 Dyspepsia 1 (13) 0 0 3 (20) 0 0 5 (36) 2 (14) 0 4 (50) 0 0 Vomiting 0 0 0 2 (13) 0 0 1 (7)  5 (36) 1 (7) 0 2 (25) 0 Hot flush 1 (13) 0 0 2 (13) 0 0 6 (43) 0 0 2 (25) 0 0 Abdominal pain 1 (13) 0 0 2 (13) 2 (13) 0 3 (21) 0 0 1 (13) 0 0 Oesophageal pain 0 0 0 0 2 (13) 0 1 (7)  3 (21) 0 1 (13) 0 0 Headache 0 0 0 3 (20) 0 0 1 (7)  1 (7)  0 3 (38) 0 0 Hiccups 0 0 0 1 (7) 0 0 4 (29) 0 0 2 (25) 0 0 Salivary hypersecretion 0 0 0 2 (13) 0 0 2 (14) 0 0 2 (25) 0 0 Diarrhoea 1 (13) 0 0 0 0 0 3 (21) 0 0 0 0 0 Dysphagia 0 0 0 0 0 0 1 (7)  2 (14) 0 3 (38) 1 (13) 0 Sensation of a foreign body 0 0 0 2 (13) 0 0 1 (7)  0 0 0 0 0 Abdominal distension 0 0 0 1 (7)  1 (7)  0 1 (7)  0 0 1 (13) 0 0 Odynophagia 0 0 0 2 (13) 0 0 1 (7)  1 (7)  0 0 0 0 Dizziness 2 (25) 0 0 1 (7)  D 0 2 (14) 0 0 1 (13) 0 0 Abdominal discomfort 0 0 0 3 (20) 0 0 0 0 0 1 (13) 1 (13) 0 Flatulence 0 0 0 2 (13) 0 0 2 (14) 0 0 1 (13) 0 0 Myalgia 1 (13) 0 0 2 (13) 1 (7)  0 0 1 (7)  0 1 (13) 0 0 1000 mg Total Active Total N = 7 N = 44 TEAE n (%) n (%) N = 44 Gr1 Gr2 Gr3 Gr1 Gr2 Gr3 All Nausea 4 (57) 2 (29) 0 14 (32)  5 (11) 0 19 (43) Dyspepsia 1 (14) 1 (14) 0 13 (30) 3 (7) 0 16 (36) Vomiting 0 3 (43) 0 3 (7) 10 (23) 1 (2) 14 (32) Hot flush 1 (14) 0 0 11 (25) 0 0 11 (25) Abdominal pain 1 (14) 1 (14) 0  7 (16) 3 (7) 0 10 (23) Oesophageal pain 1 (14) 1 (14) 1 (14) 3 (7)  6 (14) 1 (2) 10 (23) Headache 2 (29) 0 0  9 (20) 1 (2) 0 10 (23) Hiccups 2 (29) 0 0  9 (20) 0 0  9 (20) Salivary hypersecretion 2 (29) 0 0  8 (18) 0 0  8 (18) Diarrhoea 3 (43) 1 (14) 0  6 (14) 1 (2) 0  7 (16) Dysphagia 0 0 0 4 (9) 3 (7) 0  7 (16) Sensation of a foreign body 4 (57) 0 0  7 (16) 0 0  7 (16) Abdominal distension 2 (29) 0 0  5 (11) 1 (2) 0  6 (14) Odynophagia 1 (14) 1 (14) 0 4 (9) 2 (5) 0  6 (14) Dizziness 1 (14) 0 0  5 (11) 0 0  5 (11) Abdominal discomfort 0 0 0 4 (9) 1 (2) 0  5 (11) Flatulence 0 0 0  5 (11) 0 0  5 (11) Myalgia 0 0 0 3 (7) 2 (5) 0  5 (11)

TABLE 8 Pharmacokinetic parameters in a Phase 1 dose escalation study of RAD1901 (Day 7) 200 mg 500 mg 750 mg 1000 mg Parameter Statistic N = 15 N = 11 N = 6 N = 3 C_(max) Geo-Mean 49.8 197 322 540 (ng/mL) Min, Max 30.6, 85.5 105, 316 248, 420 481, 602 t_(max) (h) Median 3.00 4.00 3.00 4.00 Min, Max 2.00, 6.00 2.00-6.02 3.00, 4.00 3.00, 6.00 AUC_(0-tau) Geo-Mean 670 2927 4614 8292 (h * ng/mL) Min, Max 418, 1181 1562, 5460 3209, 7183 7281, 8947 t_(1/2) (h) Geo-Mean 38.3 37.5 38.4 42.3 Min, Max 27.7, 51.4 33.8, 41.3 34.6, 46.4 38.7, 49.4

TABLE 9 Frequency of LBD mutations Frequency (%) D538G 29.5 Y537S 25.0 Y537N 13.6 Y537C 9.1 E380Q 6.8 S463P 4.5 L536R 2.3 L536Q 2.3 P535H 2.3 V392I 2.3 V534E 2.3

TABLE 10 Differences of ER-α LBD-antagonist complexes in residue poses versus 3ERT Residue L1-3/ #/ Helix 8 Helix 11 Helix 5 Helix 12 PDB M421 I424 E521 M524 H524 L525 Y526 S527 M528 E380 Y537 L540 2BJ4 x x x x x x x NA 2JFA x x x x x x x NA 1SJ0 x x x x x x x x 2JF9 x x x x x x x NA 1YIM x x x x x x 1R5K x x x x x x X x x 1UMO x x x x 1ERR x x x x x x 2IOK x x x x x x x x 3UUC x x x x x x x x 1YIN x x x X x x x x x 2AYR x X x x 2OUZ x x x x

TABLE 11 Evaluation of structure overlap of ER-α LBD-antagonist complexes by RMSD calculations: RMSD 3ERT 2BJ4 2JFA 1SJ0 2JF9 1Y1M 1R5K 1UOM 1ERR 2IOK 3UUC 1Y1N 2AYR 3ERT 2BJ4 0.804 2JFA 1.196 0.554 1SJ0 0.786 0.637 1.115 2JF9 1.177 0.411 0.415 1.186 1Y1M 0.978 0.687 1.118 0.276 1.072 1R5K 1.483 0.759 0.52 1.307 0.892 1.342 1UOM 0.739 0.761 0.723 0.489 0.909 0.499 1.115 1ERR 1.12 0.483 0.595 1.016 0.851 1.112 1.208 0.918 2IOK 0.824 0.689 0.787 0.899 0.897 0.854 1.208 0.736 0.838 3UUC 1.024 0.915 0.896 1.03 0.888 1.036 1.228 1.012 0.873 0.929 1Y1N 0.749 0.683 1.105 0.432 1.061 0.318 1.293 0.557 1.076 0.744 1.015 2AYR 0.659 0.682 0.95 0.792 1.124 0.777 1.391 0.491 1.118 0.071 1.031 0.581

TABLE 12 Analysis of ligand binding in ER-α LBD-antagonist complexes Ligand: Binding to EC₅₀ (μM) Comments 3ERT OHT: E353, R394 0.010 Flipped amine, F404 was too far from the phenol thus there were no pi-interactions 2BJ4 OHT: E353, R394, pi 0.010 F404 2JF9 OHT: E353, D351, 0.010 H524, pi F404 2JFA RAL: E353, D351, 0.002 H524 and pi F404 x2 1ERR RAL: E353, D351, 0.002 Phenol flipped R394 and pi F404 x2 for H524 1YIM CM3: E353, H524, 0.0015(IC₅₀) D351-carboxyle D351 pi F404 oriented well with pyrrolidine 1YIN CM3: E535, H524 pi 0.001 F404 1SJ0 E4D: E353, H524, pi 0.0008(IC₅₀) F404 x 2 1R5K GW5: D351 pi F404 0.039(IC₅₀) No anchor bond with E353 1UOM PTI: E353, H524 pi NA F404 2IOK IOK: E353 pi F404 0.001 3UUC OD1: E353, R394, T347 NA Very small compound 2OUZ C3D: E353, pi F404 0.003 2AYR L4G: E353, pi F404 x2 0.0107

TABLE 13 Model evaluation for RAD1901 docking EF₅₀ Can model Ligand RAD1901 EC₅₀ (=predictive predict crystal docking docking (μM) power) structure? score score 1ERR 0.001 No −11.452 −7.912 3ERT 0.002 No −12.175 −8.151 3UCC NA 8474 Yes −9.278 NA 2IOK 0.001 Yes −11.952 −10.478 1R5K 0.039 6100 Yes −11.518 −12.102 1SJ0 0.001 7511 Yes −12.507 −9.816 2JFA 0.001 6780 Yes −11.480 −11.055 2BJ4 0.002 5642 Yes −9.727 −11.971 2OUZ 0.003 — Yes −11.789 −9.611

TABLE 14 Induced Fit Docking Score of RAD1901 with 1R5K, 1SJ0, 2IFA, 2BJ4 and 2OUZ ER-α Crystal Structure RAD1901 IFD Docking Score 1R5K −14.1 1SJ0 −13.1 2JFA −13.9 2BJ4 −13.8 2OUZ −13.4 

What is claimed is:
 1. A method of inhibiting tumor growth or producing tumor regression in a subject having a drug-resistant estrogen receptor alpha-positive cancer comprising administering to said subject a therapeutically effective amount of a combination of palbociclib and RAD1901 having the structure:

or a salt or solvate thereof.
 2. A method of inhibiting tumor growth or producing tumor regression in a subject having a mutant estrogen receptor alpha-positive cancer comprising administering to said subject a therapeutically effective amount of a combination of palbociclib and RAD1901 having the structure:

or a salt or solvate thereof.
 3. The method of claim 1 or 2, wherein the cancer is selected from the group consisting of breast cancer, uterine cancer, ovarian cancer, and pituitary cancer.
 4. The method of claim 1 or 2, wherein the cancer is a metastatic cancer.
 5. The method of claim 1 or 2, wherein said cancer is positive for the mutant estrogen receptor alpha comprising one or more mutations selected from the group consisting of Y537X₁, L536X₂, P535H, V534E, S463P, V392I, E380Q and combinations thereof, wherein: X₁ is S, N, or C, D538G; and X₂ is R or Q,
 6. The method of claim 5, wherein the mutation is Y537S.
 7. The method of claim 1 or 2, wherein the ratio of the concentration of RAD1901 or a salt or solvate thereof in the tumor to the concentration of RAD1901 or a salt or solvate thereof in plasma (T/P) following administration is at least about
 15. 8. The method of claim 1 or 2, wherein the subject has osteoporosis or a higher risk of osteoporosis.
 9. The method of claim 1 or 2, wherein the subject is a premenopausal woman.
 10. The method of claim 1 or 2, wherein the subject is a postmenopausal woman who had relapsed or progressed after previous treatment with SERMs and/or AIs.
 11. The method of claim 1 or 2, wherein the therapeutically effective amount is about 150 to about 1,500 mg q.d.
 12. The method of claim 1 or 2, wherein the salt thereof is RAD1901 dihydrochloride.
 13. The method of claim 1 or 2, wherein the tumor is resistant to a drug selected from the group consisting of anti-estrogens, aromatase inhibitors, and combinations thereof.
 14. The method of claim 13, wherein the anti-estrogen is tamoxifen or fulvestrant.
 15. The method of claim 13, wherein the aromatase inhibitors is aromasin.
 16. The method of claim 1 or 2, wherein the therapeutically effective amount is 150 mg to 2,000 mg.
 17. The method of claim 16, wherein the therapeutically effective amount is 200 mg, 400 mg, or 500 mg.
 18. A pharmaceutical composition comprising palbociclib and RAD1901 or a salt or solvate thereof.
 19. A method of treating breast cancer in a subject having a drug-resistant estrogen receptor alpha-positive cancer comprising administering to said subject a therapeutically effective amount of a combination of a cdk4/6 inhibitor and RAD1901 having the structure:

or a salt or solvate thereof.
 20. The method of claim 19 wherein said drug resistant breast cancer is resistant to one or more antiestrogen or aromatase inhibitor therapies.
 21. The method of claim 20 wherein said one or more antiestrogens are selected from the group consisting of tamoxifen, toremifene and fulvestrant and said one or more aromatase inhibitors are selected from the group consisting of aromasin, letrozole and anastrozole.
 22. The method according to any one of claims 19-21 wherein said woman expresses at least one mutant estrogen receptor alpha selected from the group consisting of D538G, Y537S, Y537N, Y537C, E380Q, S463P, L536R, L536Q, P535H, V392I and V534E.
 23. The method of claim 22 wherein said mutant estrogen receptor alpha is selected from the group consisting of Y537S, Y537N, Y537C, D538G, L536R, S463P and E380Q
 24. The method according to claim 22 or 23 wherein said mutant receptor alpha is Y537S.
 25. The method according to any one of claims 19-24 wherein said RAD1901 is administered in a total daily dosage of from between 100 mg and 1,500 mg.
 26. The method according to claim 25 wherein said RAD1901 is administered in a total daily dosage of from between 100 mg and 1,000 mg.
 27. The method according to claim 26 wherein said RAD1901 is administered in a total daily dosage of 100 mg, 200 mg, 300 mg, 400 mg, 500 mg, 600 mg, 700 mg, 800 mg, 900 mg or 1,000 mg.
 28. The method according to any one of claims 25-27 wherein said daily dosage is delivered in two separate doses.
 29. The method according to claim 28 wherein said separate doses are equal doses.
 30. The method according to claim 29 wherein said equal doses are 100 mg, 200 mg, 250 mg, 300 mg, 400 mg or 500 mg each.
 31. The method according to any of claims 25-30 wherein said dosage is delivered by the oral route.
 32. The method according to any one of claims 19-31 wherein said woman is post-menopausal.
 33. The method according to any one of claims 19-32 wherein said woman is first identified for treatment through measuring for increased expression of one or more genes selected from ABL1, AKT1, AKT2, ALK, APC, AR, ARID1A, ASXL1, ATM, AURKA, BAP, BAP1, BCL2L11, BCR, BRAF, BRCA1, BRCA2, CCND1, CCND2, CCND3, CCNE1, CDH1, CDK4, CDK6, CDK8, CDKN1A, CDKN1B, CDKN2A, CDKN2B, CEBPA, CTNNB1, DDR2, DNMT3A, E2F3, EGFR, EML4, EPHB2, ERBB2, ERBB3, ESR1, EWSR1, FBXW7, FGF4, FGFR1, FGFR2, FGFR3, FLT3, FRS2, HIF1A, HRAS, IDH1, IDH2, IGF1R, JAK2, KDM6A, KDR, KIF5B, KIT, KRAS, LRP1B, MAP2K1, MAP2K4, MCL1, MDM2, MDM4, MET, MGMT, MLL, MPL, MSH6, MTOR, MYC, NF1, NF2, NKX2-1, NOTCH1, NPM, NRAS, PDGFRA, PIK3CA, PIK3R1, PML, PTEN, PTPRD, RARA, RB1, RET, RICTOR, ROS1, RPTOR, RUNX1, SMAD4, SMARCA4, SOX2, STK11, TET2, TP53, TSC1, TSC2, and VHL.
 34. The method according to claim 33 wherein said one or more genes is selected from AKT1, AKT2, BRAF, CDK4, CDK6, PIK3CA, PIK3R1 and MTOR.
 35. The method according to any of claims 19-34 wherein said cdk4/cdk6 inhibitor is selected from the group consisting of abemaciclib, ribociclib and palbociclib.
 36. The method according to claim 35 wherein said cdk4/6 inhibitor is palbociclib.
 37. The method according to claim 36 wherein said palbociclib is dosed at a daily dose of from between 25 mg and 250 mg.
 38. The method according to claim 37 wherein said palbociclib is dosed at a daily dose of from between 50 to 125 mg.
 39. The method according to claim 37 wherein said palbociclib is dosed at a daily dose of from between 75 mg to 125 mg.
 40. The method according to claim 37 wherein said palbociclib is dosed at 75 mg, 100 mg or 125 mg daily.
 41. The method according to claim 37 wherein said palbociclib is dosed at a daily dose of from between 31.25 mg to 93.75 mg.
 42. The method according to any one of claims 36-41 wherein said palbociclib is dosed for 21 days in a 28 day cycle.
 43. The method according to any one of claims 36-41 wherein said palbociclib is dosed less than 21 days in a 28 day cycle.
 44. The method according to any one of claims 36-41 wherein said palbociclib is dosed from between 7 days and 20 days in a 28 day cycle.
 45. The method according to any one of claims 36-41 wherein said palbociclib is dosed 7 days or 14 days of a 28 day cycle.
 46. The method according to claim 36 wherein said palbociclib is dosed in a total amount of 2,625 mg in a 28 day cycle.
 47. The method according to claim 36 wherein said palbociclib is dosed in a total amount of from between 656.25 mg and 1,968.75 mg in a 28 day cycle.
 48. The method according to claim 35 wherein said cdk4/6 inhibitor is ribociclib.
 49. The method according to claim 48 wherein said ribociclib is dosed at a daily dose of from between 200 mg and 1,000 mg.
 50. The method according to claim 49 wherein said ribociclib is dosed at a daily dose of from between 250 to 750 mg.
 51. The method according to claim 50 wherein said ribociclib is dosed at a daily dose of 600 mg.
 52. The method according to claim 48 wherein said ribociclib is dosed at a daily dose of from between 150 mg to 450 mg.
 53. The method according to any one of claims 48-52 wherein said ribociclib is dosed for 21 days in a 28 day cycle.
 54. The method according to any one of claims 48-52 wherein said ribociclib is dosed less than 21 days in a 28 day cycle.
 55. The method according to any one of claim 54 wherein said ribociclib is dosed from between 7 days and 20 days in a 28 day cycle.
 56. The method according to any one of claim 55 wherein said ribociclib is dosed 7 days or 14 days of a 28 day cycle.
 57. The method according to claim 48 wherein said ribociclib is dosed in a total amount of 12,600 mg in a 28 day cycle.
 58. The method according to claim 48 wherein said ribociclib is dosed in a total amount of from between 3,150 mg and 9,450 mg in a 28 day cycle.
 59. The method according to any one of claims 35-58 wherein said ribociclib or said palbociclib is dosed orally.
 60. The method according to claim 59 wherein said ribociclib and said palbociclib are dosed orally once per day.
 61. The method according to claim 34 wherein said cdk4/6 inhibitor is abemaciclib.
 62. The method according to claim 61 wherein said abemaciclib is dosed at a daily dose of 300 mg.
 63. The method according to claim 61 wherein said abemaciclib is dosed at a daily dose of 150 mg twice daily.
 64. The method according to any one of claims 61-63 wherein said abemaciclib is dosed for 28 days in a 28 day cycle.
 65. The method according to any one of claims 61-63 wherein said abemaciclib is dosed less than 28 days in a 28 day cycle.
 66. The method according to claim 65 wherein said abemaciclib is dosed from between 21 days and 27 days in a 28 day cycle.
 67. The method according to claim 65 wherein said abemaciclib is dosed 7 days or 14 or 21 days of a 28 day cycle.
 68. The method according to claim 61 wherein said abemaciclib is dosed in a total amount of 8,400 mg in a 28 day cycle.
 69. The method according to claim 61 wherein said abemaciclib is dosed in a total amount of from between 2,100 mg and 6,300 mg in a 28 day cycle.
 70. The method according to any one of claims 61-69 wherein said abemaciclib is dosed orally. 